[2641] Add doc for get_num_users()

src/bin/cmdctl/cmdctl.py.in

@@ -541,6 +541,7 @@ class SecureHTTPServer(socketserver_mixin.NoPollMixIn,
         return info
 
     def get_num_users(self):
+        ''' Returns the number of users known to the server. '''
         with self._lock:
             num = len(self._user_infos)
         return num