Improve comments on get_user_by_access_token

because I have to reverse-engineer this every time.

synapse/api/auth.py

@@ -270,7 +270,11 @@ class Auth(object):
             rights (str): The operation being performed; the access token must
                 allow this.
         Returns:
-            dict : dict that includes the user and the ID of their access token.
+            Deferred[dict]: dict that includes:
+               `user` (UserID)
+               `is_guest` (bool)
+               `token_id` (int|None): access token id. May be None if guest
+               `device_id` (str|None): device corresponding to access token
         Raises:
             AuthError if no user by that token exists or the token is invalid.
         """