@classmethod
  @gen.coroutine
  def _FormatAddFollowersText(cls, client, viewpoint, activity):
    sharer_name = yield AlertManager._GetNameFromUserId(client, activity.user_id)
    raise gen.Return('%s added you to a conversation%s' % (sharer_name, AlertManager._GetViewpointTitle(viewpoint)))
Constructs the alert text for an "add_followers" operation, similar to this:
dataset/ETHPy150Open viewfinderco/viewfinder/backend/op/alert_manager.py/AlertManager._FormatAddFollowersText