Include a default configuration file in the 'docs' directory. (#4791)

scripts/generate_config

@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import argparse
+import shutil
 import sys
 
 from synapse.config.homeserver import HomeServerConfig
@@ -50,6 +51,13 @@ if __name__ == "__main__":
         help="File to write the configuration to. Default: stdout",
     )
 
+    parser.add_argument(
+        "--header-file",
+        type=argparse.FileType('r'),
+        help="File from which to read a header, which will be printed before the "
+             "generated config.",
+    )
+
     args = parser.parse_args()
 
     report_stats = args.report_stats
@@ -64,4 +72,7 @@ if __name__ == "__main__":
         report_stats=report_stats,
     )
 
+    if args.header_file:
+        shutil.copyfileobj(args.header_file, args.output_file)
+
     args.output_file.write(conf)