code: func BootstrapWithMultiRegions(cluster *Cluster, splitKeys ...[]byte) (storeID uint64, regionIDs, peerIDs []uint64) {
  	var firstRegionID, firstPeerID uint64
  	storeID, firstPeerID, firstRegionID = BootstrapWithSingleStore(cluster)
  	regionIDs = append([]uint64{firstRegionID}, cluster.AllocIDs(len(splitKeys))...)
  	peerIDs = append([]uint64{firstPeerID}, cluster.AllocIDs(len(splitKeys))...)
  	for i, k := range splitKeys {
  		cluster.Split(regionIDs[i], regionIDs[i+1], k, []uint64{peerIDs[i]}, peerIDs[i])
  	}
  	return
  }
docs: // BootstrapWithMultiRegions initializes a Cluster with multiple Regions and 1
  // Store. The number of Regions will be len(splitKeys) + 1.