Add link for get_protocol_members

Author: brianschubert

doc/index.rst

@@ -846,6 +846,8 @@ Functions
 
 .. function:: get_protocol_members(tp)
 
+   See :py:func:`typing.get_protocol_members`. In ``typing`` since 3.13.
+
    Return the set of members defined in a :class:`Protocol`. This works with protocols
    defined using either :class:`typing.Protocol` or :class:`typing_extensions.Protocol`.