Document how to use a customer gRPC port.

Getting-Started.md

@@ -38,6 +38,7 @@ Usually you would need to specify the available disk space, the Weed Master loca
 ```bash
 ./weed volume -max=100 -mserver="localhost:9333" -dir="./data"
 ```
+If you are using a custom gRPC port for master, the address format for `mserver` is `<host>:<port>.<grpcPort>`.
 
 ### Cheat Sheet: Setup One Master Server and One Volume Server