code: func (n *Node) SubscribeLeadership() (q chan events.Event, cancel func()) {
  	return n.leadershipBroadcast.Watch()
  }
docs: // SubscribeLeadership returns channel to which events about leadership change
  // will be sent in form of raft.LeadershipState. Also cancel func is returned -
  // it should be called when listener is no longer interested in events.