code: def link_rich_menu_to_user(self, user_id, rich_menu_id, timeout=None):
          
          self._post(
              '/v2/bot/user/{user_id}/richmenu/{rich_menu_id}'.format(
                  user_id=user_id,
                  rich_menu_id=rich_menu_id
              ),
              timeout=timeout
          )
docs: Call link rich menu to user API.
  
          https://developers.line.me/en/docs/messaging-api/reference/#link-rich-menu-to-user
  
          :param str user_id: ID of an uploaded rich menu
          :param str rich_menu_id: ID of the user
          :type timeout: float | tuple(float, float)