chore(volumes): modify volumes:client cmd annotation

Author: jianxiaoguo

parser/volumes.go

@@ -233,6 +233,7 @@ Arguments:
     rm         remove volume files
   <args>
     arguments for running commands
+    volume path format 'vol://volumename/', '/' is equivalent to the mount path.
 
 Options:
   -a --app=<app>