Fixup broken links

```
dmr on titan in synapse/book on  dmr/docs-tidy via  v16.14.0 via 🐍 v3.10.7 (matrix-synapse-py3.10) via 🐏 12GiB/15GiB | 5GiB/8GiB took 8s
2022-10-24 15:15:53 ✔  $ linkchecker **.html
INFO linkcheck.cmdline 2022-10-24 15:16:33,785 MainThread Checking intern URLs only; use --check-extern to check extern URLs.
LinkChecker 10.1.0
Copyright (C) 2000-2016 Bastian Kleineidam, 2010-2021 LinkChecker Authors
LinkChecker comes with ABSOLUTELY NO WARRANTY!
This is free software, and you are welcome to redistribute it under
certain conditions. Look at the file `LICENSE' within this distribution.
Read the documentation at https://linkchecker.github.io/linkchecker/
Write comments and bugs to https://github.com/linkchecker/linkchecker/issues

Start checking at 2022-10-24 15:16:33+001
/usr/lib/python3.10/site-packages/bs4/__init__.py:435: MarkupResemblesLocatorWarning: The input looks more like a filename than markup. You may want to open this file and pass the filehandle into Beautiful Soup.
  warnings.warn(
10 threads active,    88 links queued,  241 links in 339 URLs checked, runtime 1 seconds

Statistics:
Downloaded: 4.04MB.
Content types: 7 image, 106 text, 0 video, 0 audio, 22 application, 3 mail and 508 other.
URL lengths: min=16, max=256, avg=67.

That's it. 646 links in 646 URLs checked. 0 warnings found. 0 errors found.
Stopped checking at 2022-10-24 15:16:39+001 (5 seconds)
```

docs/administration/admin_api/account_validity.md

@@ -5,7 +5,7 @@ use it, you must enable the account validity feature (under
 `account_validity`) in Synapse's configuration.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 ## Renew account
 

docs/administration/admin_api/event_reports.md

@@ -3,7 +3,7 @@
 This API returns information about reported events.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 The api is:
 ```

docs/administration/admin_api/federation.md

@@ -81,7 +81,7 @@ The following fields are returned in the JSON response body:
   - `failure_ts` - nullable integer - The first time Synapse tried and failed to reach the
     remote server, in ms. This is `null` if communication with the remote server has never failed.
   - `last_successful_stream_ordering` - nullable integer - The stream ordering of the most
-    recent successfully-sent [PDU](understanding_synapse_through_grafana_graphs.md#federation)
+    recent successfully-sent [PDU](../understanding_synapse_through_grafana_graphs.md#federation)
     to this destination, or `null` if this information has not been tracked yet.
 - `next_token`: string representing a positive integer - Indication for pagination. See above.
 - `total` - integer - Total number of destinations.
@@ -174,7 +174,7 @@ The following fields are returned in the JSON response body:
   Room objects contain the following fields:
   - `room_id` - string - The ID of the room.
   - `stream_ordering` - integer -  The stream ordering of the most recent
-    successfully-sent [PDU](understanding_synapse_through_grafana_graphs.md#federation)
+    successfully-sent [PDU](../understanding_synapse_through_grafana_graphs.md#federation)
     to this destination in this room.
 - `next_token`: string representing a positive integer - Indication for pagination. See above.
 - `total` - integer - Total number of destinations.

docs/administration/admin_api/media_admin_api.md

@@ -6,7 +6,7 @@ Details about the format of the `media_id` and storage of the media in the file
 are documented under [media repository](../../development/internal_documentation/media_repository.md).
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 ## List all media in a room
 

docs/administration/admin_api/purge_history_api.md

@@ -11,7 +11,7 @@ Note that Synapse requires at least one message in each room, so it will never
 delete the last message in a room.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 The API is:
 

docs/administration/admin_api/registration_tokens.md

@@ -6,7 +6,7 @@ registration requests, as proposed in
 and stabilised in version 1.2 of the Matrix specification.
 To use it, you will need to enable the `registration_requires_token` config
 option, and authenticate by providing an `access_token` for a server admin:
-see [Admin API](../usage/administration/admin_api).
+see [Admin API](index.html).
 
 
 ## Registration token objects

docs/administration/admin_api/room_membership.md

@@ -6,7 +6,7 @@ local users. The server administrator must be in the room and have permission to
 invite users.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 ## Parameters
 

docs/administration/admin_api/rooms.md

@@ -5,7 +5,7 @@ server. There are various parameters available that allow for filtering and
 sorting the returned list. This API supports pagination.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 **Parameters**
 
@@ -400,7 +400,7 @@ sent to a room in a given timeframe. There are various parameters available
 that allow for filtering and ordering the returned list. This API supports pagination.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 This endpoint mirrors the [Matrix Spec defined Messages API](https://spec.matrix.org/v1.1/client-server-api/#get_matrixclientv3roomsroomidmessages).
 

docs/administration/admin_api/statistics.md

@@ -4,7 +4,7 @@ Returns information about all local media usage of users. Gives the
 possibility to filter them by time and user.
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 The API is:
 

docs/administration/admin_api/user_admin_api.md

@@ -1,7 +1,7 @@
 # User Admin API
 
 To use it, you will need to authenticate by providing an `access_token`
-for a server admin: see [Admin API](../usage/administration/admin_api).
+for a server admin: see [Admin API](index.html).
 
 ## Query User Account
 

docs/administration/admin_faq.md

@@ -115,7 +115,7 @@ something like the following in their logs:
 
     2019-09-11 19:32:04,271 - synapse.federation.transport.server - 288 - WARNING - GET-11752 - authenticate_request failed: 401: Invalid signature for server <server> with key ed25519:a_EqML: Unable to verify signature for <server>
 
-This is normally caused by a misconfiguration in your reverse-proxy. See [the reverse proxy docs](docs/reverse_proxy.md) and double-check that your settings are correct.
+This is normally caused by a misconfiguration in your reverse-proxy. See [the reverse proxy docs](../setup/reverse_proxy.md) and double-check that your settings are correct.
 
 
 Help!! Synapse is slow and eats all my RAM/CPU!

docs/administration/request_log.md

@@ -1,6 +1,6 @@
 # Request log format
 
-HTTP request logs are written by synapse (see [`site.py`](../synapse/http/site.py) for details).
+HTTP request logs are written by synapse (see [`site.py`](https://github.com/matrix-org/synapse/blob/latest/synapse/http/site.py) for details).
 
 See the following for how to decode the dense data available from the default logging configuration.
 

docs/usage/configuration/workers.md

@@ -153,7 +153,7 @@ Finally, you need to start your worker processes. This can be done with either
 `synctl` or your distribution's preferred service manager such as `systemd`. We
 recommend the use of `systemd` where available: for information on setting up
 `systemd` to start synapse workers, see
-[Systemd with Workers](systemd-with-workers). To use `synctl`, see
+[Systemd with Workers](systemd-with-workers/index.html). To use `synctl`, see
 [Using synctl with Workers](synctl_workers.md).