code: func (n *Network) PeerGroupRunner() ifrit.Runner {
  	members := grouper.Members{}
  	for _, p := range n.Peers {
  		members = append(members, grouper.Member{Name: p.ID(), Runner: n.PeerRunner(p)})
  	}
  	return grouper.NewParallel(syscall.SIGTERM, members)
  }
docs: // PeerGroupRunner returns a runner that can be used to start and stop all
  // peers in a network.