Machine-readable config description (#17892)

docs/README.md

@@ -63,6 +63,18 @@ mdbook serve
 
 The URL at which the docs can be viewed at will be logged.
 
+## Synapse configuration documentation
+
+The [Configuration
+Manual](https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html)
+page is generated from a YAML file,
+[schema/synapse-config.schema.yaml](../schema/synapse-config.schema.yaml). To
+add new options or modify existing ones, first edit that file, then run
+[scripts-dev/gen_config_documentation.py](../scripts-dev/gen_config_documentation.py)
+to generate an updated Configuration Manual markdown file.
+
+Build the book as described above to preview it in a web browser.
+
 ## Configuration and theming
 
 The look and behaviour of the website is configured by the [book.toml](../book.toml) file

docs/usage/administration/admin_faq.md

@@ -255,7 +255,7 @@ line to `/etc/default/matrix-synapse`:
 
     LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2
 
-*Note*: You may need to set `PYTHONMALLOC=malloc` to ensure that `jemalloc` can accurately calculate memory usage. By default, Python uses its internal small-object allocator, which may interfere with jemalloc's ability to track memory consumption correctly. This could prevent the [cache_autotuning](../configuration/config_documentation.md#caches-and-associated-values) feature from functioning as expected, as the Python allocator may not reach the memory threshold set by `max_cache_memory_usage`, thus not triggering the cache eviction process.
+*Note*: You may need to set `PYTHONMALLOC=malloc` to ensure that `jemalloc` can accurately calculate memory usage. By default, Python uses its internal small-object allocator, which may interfere with jemalloc's ability to track memory consumption correctly. This could prevent the [cache_autotuning](../configuration/config_documentation.md#caches) feature from functioning as expected, as the Python allocator may not reach the memory threshold set by `max_cache_memory_usage`, thus not triggering the cache eviction process.
 
 This made a significant difference on Python 2.7 - it's unclear how
 much of an improvement it provides on Python 3.x.