update readme (#976)

README.md

@@ -13,7 +13,8 @@ Gin is a web framework written in Go (Golang). It features a martini-like API wi
 ![Gin console logger](https://gin-gonic.github.io/gin/other/console.png)
 
 ```sh
-$ cat test.go
+# assume the following codes in example.go file
+$ cat example.go
 ```
 
 ```go
@@ -32,6 +33,11 @@ func main() {
 }
 ```
 
+```
+# run example.go and visit 0.0.0.0:8080/ping on browser
+$ go run example.go
+```
+
 ## Benchmarks
 
 Gin uses a custom version of [HttpRouter](https://github.com/julienschmidt/httprouter)