doc(readme): add additional middleware doc.

README.md

@@ -369,6 +369,7 @@ r := gin.New()
 instead of
 
 ```go
+// Default With the Logger and Recovery middleware already attached
 r := gin.Default()
 ```
 
@@ -380,7 +381,10 @@ func main() {
 	r := gin.New()
 
 	// Global middleware
+	// Logger middleware will write the logs to gin.DefaultWriter even you set with GIN_MODE=release. By default gin.DefaultWriter = os.Stdout
 	r.Use(gin.Logger())
+	
+	// Recovery middleware recovers from any panics and writes a 500 if there was one.
 	r.Use(gin.Recovery())
 
 	// Per route middleware, you can add as many as you desire.