📝 Update README with gitter chat

Add gitter chat for questions and problems.

Author: apertureless

README.md

@@ -7,6 +7,7 @@
 [![Build Status](https://travis-ci.org/apertureless/vue-chartjs.svg?branch=master)](https://travis-ci.org/apertureless/vue-chartjs)
 [![Package Quality](http://npm.packagequality.com/shield/vue-chartjs.svg)](http://packagequality.com/#?package=vue-chartjs)
 [![npm](https://img.shields.io/npm/dm/localeval.svg)](https://www.npmjs.com/package/vue-chartjs)
+[![Gitter chat](https://badges.gitter.im/gitterHQ/gitter.png)](https://gitter.im/vue-chartjs/Lobby)
 [![license](https://img.shields.io/github/license/mashape/apistatus.svg)](https://github.com/apertureless/vue-chartjs/blob/master/LICENSE.txt)
 
 # vue-chartjs