docs: def add_watcher(self, issue, watcher):
          """Add a user to an issue's watchers list.
  
          :param issue: ID or key of the issue affected
          :param watcher: username of the user to add to the watchers list
          """
          url = self._get_url('issue/' + str(issue) + '/watchers')
          self._session.post(
              url, data=json.dumps(watcher))