New example for the JSONP middleware

Author: ant0ine

README.md

@@ -24,6 +24,7 @@
 	  - [API and static files](#api-and-static-files)
 	  - [GORM](#gorm)
 	  - [CORS](#cors)
+	  - [JSONP](#jsonp)
 	  - [Basic Auth](#basic-auth)
 	  - [Status](#status)
 	  - [Status Auth](#status-auth)
@@ -680,6 +681,54 @@ func GetAllCountries(w rest.ResponseWriter, r *rest.Request) {
 
 ```
 
+#### JSONP
+
+Demonstrate how to use the JSONP middleware.
+
+The curl demo:
+``` sh
+curl -i http://127.0.0.1:8080/message
+curl -i http://127.0.0.1:8080/message?cb=parseResponse
+```
+
+
+Go code:
+``` go
+package main
+
+import (
+	"github.com/ant0ine/go-json-rest/rest"
+	"log"
+	"net/http"
+)
+
+type Message struct {
+	Body string
+}
+
+func main() {
+	handler := rest.ResourceHandler{
+		PreRoutingMiddlewares: []rest.Middleware{
+			&rest.JsonpMiddleware{
+				CallbackNameKey: "cb",
+			},
+		},
+	}
+	err := handler.SetRoutes(
+		&rest.Route{"GET", "/message", func(w rest.ResponseWriter, req *rest.Request) {
+			w.WriteJson(&Message{
+				Body: "Hello World!",
+			})
+		}},
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+	log.Fatal(http.ListenAndServe(":8080", &handler))
+}
+
+```
+
 #### Basic Auth
 
 Demonstrate how to setup AuthBasicMiddleware as a pre-routing middleware.