chore(docs): clarify token type usage with auth()

docs/api-usage.rst

@@ -38,7 +38,8 @@ To connect to GitLab.com or another GitLab instance, create a ``gitlab.Gitlab``
    gl = gitlab.Gitlab('https://gitlab.example.com', user_agent='my-package/1.0.0')
 
    # make an API request to create the gl.user object. This is mandatory if you
-   # use the username/password authentication (not required for job token authentication).
+   # use the username/password authentication - not required for token authentication,
+   # and will not work with job tokens.
    gl.auth()
 
 You can also use configuration files to create ``gitlab.Gitlab`` objects: