request doc changes

docs/usage/configuration/config_documentation.md

@@ -1867,11 +1867,13 @@ Config options related to Synapse's media store.
 ### `enable_authenticated_media`
 
 When set to true, all subsequent media uploads will be marked as authenticated, and will not be available over legacy
-unauthenticated media endpoints (`/_matrix/media/(r0|v3|v1)/download` and `/_matrix/media/(r0|v3|v1)/thumbnail`) - requests for authenticated media over these endpoints will result in a 404. All media, including authenticated media, will be available over the authenticated media endpoints `_matrix/client/v1/media/download` and `_matrix/client/v1/media/thumbnail`. Media uploaded prior to setting this option to true will still be available over the legacy endpoints.
+unauthenticated media endpoints (`/_matrix/media/(r0|v3|v1)/download` and `/_matrix/media/(r0|v3|v1)/thumbnail`) - requests for authenticated media over these endpoints will result in a 404. All media, including authenticated media, will be available over the authenticated media endpoints `_matrix/client/v1/media/download` and `_matrix/client/v1/media/thumbnail`. Media uploaded prior to setting this option to true will still be available over the legacy endpoints. Note if the setting is switched to false
+after enabling, media marked as authenticated will be available over legacy endpoints. Defaults to false, but
+this will change to true in a future Synapse release.
 
 Example configuration:
 ```yaml
-enable_authenticated_media
+enable_authenticated_media: true
 ```
 ---
 ### `enable_media_repo`