docs(readme): add Greenkeeper badge

Author: greenkeeper[bot]

README.md

@@ -1,5 +1,7 @@
 # Parse Dashboard
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/parse-community/parse-dashboard.svg)](https://greenkeeper.io/)
+
 [![Build Status](https://img.shields.io/travis/parse-community/parse-dashboard/master.svg?style=flat)](https://travis-ci.org/parse-community/parse-dashboard)
 [![npm version](https://img.shields.io/npm/v/parse-dashboard.svg?style=flat)](https://www.npmjs.com/package/parse-dashboard)