re-add note about the login process

Author: turt2live

specification/client_server_api.rst

@@ -1097,7 +1097,8 @@ process. The page will attempt to call the JavaScript function
 ``window.onLogin`` when login has been successfully completed.
 
 Non-credential parameters valid for the ``/login`` endpoint can be provided as query
-string parameters here. For example::
+string parameters here. These are to be forwarded to the login endpoint during the login
+process. For example::
 
     GET /_matrix/static/client/login/?device_id=GHTYAJCE