code: func (n *Node) applyAddNode(cc raftpb.ConfChange) error {
  	member := &api.RaftMember{}
  	err := proto.Unmarshal(cc.Context, member)
  	if err != nil {
  		return err
  	}
  
  	// ID must be non zero
  	if member.RaftID == 0 {
  		return nil
  	}
  
  	return n.registerNode(member)
  }
docs: // applyAddNode is called when we receive a ConfChange
  // from a member in the raft cluster, this adds a new
  // node to the existing raft cluster