add screenshot to readme

Author: ntamvl

README.md

@@ -16,6 +16,9 @@ This how-to guide aims to help you get started the right way using Rails 5 to bu
 *   [Authenticating Your API](#authenticating-your-api)
 *   [API documentation use Swagger UI](#documenting-rails-based-rest-api-using-swagger-ui)
 
+## Screenshot
+![Building the Perfect Rails 5 API Only using Swagger UI for documentation](https://c7.staticflickr.com/9/8548/29979999550_7980b15a45_b.jpg)
+
 ## Setting up Rails 5
 
 First, make sure you are running Ruby 2.2.2+ or newer as it’s required by Rails 5.