add basic usage string

Author: ggilmore

proxy.go

@@ -51,6 +51,11 @@ func (h jsonrpc2HandlerFunc) Handle(ctx context.Context, conn *jsonrpc2.Conn, re
 }
 
 func main() {
+	flag.Usage = func() {
+		fmt.Printf("Usage: cloneproxy [OPTIONS] [LSP_COMMAND_ARGS...]\n\nOptions:\n")
+		flag.PrintDefaults()
+	}
+
 	flag.Parse()
 	log.SetFlags(log.Flags() | log.Lshortfile)