docs: clarify no login rate limit for roundup-xmlrpc-server

Login rate limit only available for /xmlrpc endpoint not supplied by
roundup-xmlrpc-server endpoint.

Author: rouilj

doc/xmlrpc.txt

@@ -93,7 +93,11 @@ Rate Limiting Failed Logins
 
 See the `rest documentation
 <rest.html#rate-limiting-api-failed-logins>`_ for rate limiting failed
-logins on the API. The XML-RPC uses the same method as the REST API.
+logins on the API. There is no login rate limiting for the standalone
+roundup-xmlrpc-server. Login rate limiting is only for the `/xmlrpc``
+endpoint when the Roundup server is used.
+
+The XML-RPC uses the same method as the REST API.
 Rate limiting is shared between the XMLRPC and REST APIs.
 
 Client API