docs(readme): add Greenkeeper badge

Author: greenkeeper[bot]

README.md

@@ -1,5 +1,7 @@
 # eDEX-UI
 
+[![Greenkeeper badge](https://badges.greenkeeper.io/GitSquared/edex-ui.svg)](https://greenkeeper.io/)
+
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/93b816722c4e4af2bdf401b8187b8a2d)](https://www.codacy.com/app/GitSquared/edex-ui?utm_source=github.com&utm_medium=referral&utm_content=GitSquared/edex-ui&utm_campaign=Badge_Grade)  [![Dependency Status](https://gemnasium.com/badges/github.com/GitSquared/edex-ui.svg)](https://gemnasium.com/github.com/GitSquared/edex-ui)   [![Build Status](https://travis-ci.org/GitSquared/edex-ui.svg?branch=master)](https://travis-ci.org/GitSquared/edex-ui)
 
 A Sci-fi interactive desktop interface heavily inspired from [DEX-UI](https://github.com/seenaburns/dex-ui) and the [TRON Legacy movie effects](http://jtnimoy.com/blogs/projects/14881671), made cross-platform and easy to install with [Electron](https://github.com/electron/electron).