Updated FAQ (markdown)

FAQ.md

@@ -109,9 +109,22 @@ Usually the logs are collected during a long period of time span. Let's say each
     /logs/2015-01-04.log
 
 ## gRPC Ports
-gRPC can be derived from the `-port` number and adding 10000 ontop of it. 
+gRPC can be derived from the `-port` number and adding 10000 on top of it. 
 `-port=8080` => gRPC Port: `18080`
 
+If you **must** have custom gRPC port, when `master`, `volume server` or `filer` starts, you can specify a custom gRPC port. Also, for all the other places referencing `master` and `filer`, you need to specify in this format
+```
+ <host>:<port>.<grpcPort>
+```
+For example:
+```
+ weed master -port=9333 -port.grpc=9444
+ weed volume -port=8080 -port.grpc=8444 -msever=localhost:9333.9444
+ weed filer  -port=8888 -port.grpc=9999 -master=localhost:9333.9444
+ weed shell -filer=localhst:8888.9999 -master=localhost:9333.9444
+ weed mount -dir=mm -filer=localhst:8888.9999
+```
+
 ## Support ipv6?
 Yes. A common error is when binding a link-scoped ipv6 address without a proper scope. This will cause `connect: invalid argument`.