Fixup docs

changelog.d/6332.bugfix

@@ -1 +1 @@
-Fix caching devices for remote users when using workers.
+Fix caching devices for remote users when using workers, so that we don't attempt to refetch (and potentially fail) each time a user requests devices.

synapse/replication/http/devices.py

@@ -21,7 +21,11 @@ logger = logging.getLogger(__name__)
 
 
 class ReplicationUserDevicesResyncRestServlet(ReplicationEndpoint):
-    """Notifies that a user has joined or left the room
+    """Ask master to resync the device list for a user by contacting their
+    server.
+
+    This must happen on master so that the results can be correctly cached in
+    the database and streamed to workers.
 
     Request format: