add example for the simple context#WriteGzip

Former-commit-id: 3b4e0834370ebde5e4796b3d75cdbd5c2c25093f

_examples/http_responsewriter/write-gzip/main.go

@@ -0,0 +1,21 @@
+package main
+
+import "github.com/kataras/iris"
+
+func main() {
+	app := iris.New()
+	app.Get("/", func(ctx iris.Context) {
+		ctx.WriteGzip([]byte("Hello World!"))
+		ctx.Header("X-Custom",
+			"Headers can be set here after WriteGzip as well, because the data are kept before sent to the client when using the context's GzipResponseWriter and ResponseRecorder.")
+	})
+
+	app.Get("/2", func(ctx iris.Context) {
+		// same as the `WriteGzip`.
+		// However GzipResponseWriter gives you more options, like
+		// reset data, disable and more, look its methods.
+		ctx.GzipResponseWriter().WriteString("Hello World!")
+	})
+
+	app.Run(iris.Addr(":8080"))
+}