simplify type definition in readme (#896)

* better text rendering

* simplify type definition in readme

readme.md

@@ -112,13 +112,15 @@ go get -u github.com/tal-tech/go-zero
 2. create the API file, like greet.api, you can install the plugin of goctl in vs code, api syntax is supported.
 
    ```go
-   type Request struct {
-     Name string `path:"name,options=you|me"` // parameters are auto validated
-   }
+   type (
+     Request {
+       Name string `path:"name,options=you|me"` // parameters are auto validated
+     }
    
-   type Response struct {
-     Message string `json:"message"`
-   }
+     Response {
+       Message string `json:"message"`
+     }
+   )
    
    service greet-api {
      @handler GreetHandler