raftexample: update readme
raftexample: update readme

mqliang/etcd,rnaveiras/etcd,cockroachdb/etcd,coreos/etcd,ajityagaty/etcd,etcd-io/etcd,mkumatag/etcd,dannysauer/etcd,mkumatag/etcd,ajityagaty/etcd,dannysauer/etcd,cockroachdb/etcd,li-ang/etcd,ajityagaty/etcd,etcd-io/etcd,mqliang/etcd,coreos/etcd,mqliang/etcd,etcd-io/etcd,mkumatag/etcd,li-ang/etcd,rnaveiras/etcd,rnaveiras/etcd,gyuho/etcd,gyuho/etcd