Add CircleCI badge to README

Author: Jeremy Wiebe

README.md

@@ -3,6 +3,7 @@
 A repo to document code standards for different languages and provide tools for linting Mobify projects.
 
 [![NPM version](https://badge.fury.io/js/mobify-code-style.svg)](http://badge.fury.io/js/mobify-code-style)
+[![CircleCI](https://circleci.com/gh/mobify/mobify-code-style/tree/develop.svg?style=svg)](https://circleci.com/gh/mobify/mobify-code-style/tree/develop)
 
 ## JavaScript (ES5) with Grunt