Update README.md

cmd/mcping/README.md

@@ -2,7 +2,8 @@
 适用于Minecraft: Java Edition的ping工具
 
 Install with go tools:  
-    ```go install github.com/Tnze/go-mc/cmd/mcping```
+    ```go get -u github.com/Tnze/go-mc/cmd/mcping```
+    `$GOPATH/bin` should in your `$PATH`.
 
 Install with Homebrew:  
     ```brew tap Tnze/tap && brew install mcping```