Currently there is a separate file for the purge remote media API docs and the rest of the media APIs
https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_remote_media.rst
https://github.com/matrix-org/synapse/blob/master/docs/admin_api/media_admin_api.md

There is also separate files for the purge room API, shutdown room API, and then the rest of the room APIs
https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_room.md
https://github.com/matrix-org/synapse/blob/master/docs/admin_api/shutdown_room.md
https://github.com/matrix-org/synapse/blob/master/docs/admin_api/rooms.md

It probably makes sense for all of the media APIs to be in one file and all of the room APIs to be in another, rather than being spread out like this.