Add a CodeTriage badge to magento/magento2

 - Additionally updated Travis CI branch link

README.md

@@ -1,4 +1,5 @@
-[![Build Status](https://travis-ci.org/magento/magento2.svg?branch=develop)](https://travis-ci.org/magento/magento2)
+[![Build Status](https://travis-ci.org/magento/magento2.svg?branch=2.2-develop)](https://travis-ci.org/magento/magento2)
+[![Open Source Helpers](https://www.codetriage.com/magento/magento2/badges/users.svg)](https://www.codetriage.com/magento/magento2)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/magento/magento2?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 [![Crowdin](https://d322cqt584bo4o.cloudfront.net/magento-2/localized.png)](https://crowdin.com/project/magento-2)
 <h2>Welcome</h2>