Fix specifying only access token

mastodon/Mastodon.py

@@ -189,7 +189,8 @@ class Mastodon:
                  version_check_mode = "created"):
         """
         Create a new API wrapper instance based on the given `client_secret` and `client_id`. If you
-        give a `client_id` and it is not a file, you must also give a secret.
+        give a `client_id` and it is not a file, you must also give a secret. If you specify an
+        `access_token` then you don't need to specify a `client_id`.
 
         You can also specify an `access_token`, directly or as a file (as written by `log_in()`_).