fix according to comments

go/cmd/pserver/pserver.go

@@ -32,7 +32,7 @@ import (
 
 func main() {
 	port := flag.Int("port", 0, "port of the pserver")
-	index := flag.Int("index", -1, "index of this pserver, should be larger or equal than 0")
+	index := flag.Int("index", -1, "index of the pserver, set to -1 if use etcd for auto pserver index registry")
 	etcdEndpoint := flag.String("etcd-endpoint", "http://127.0.0.1:2379",
 		"comma separated endpoint string for pserver to connect to etcd")
 	dialTimeout := flag.Duration("dial-timeout", 5*time.Second, "dial timeout")