Update README with Ember Observer badge + score

Author: Sticksword

README.md

@@ -1,6 +1,7 @@
 # Ember Chart
 
 [![Build Status](https://travis-ci.org/aomran/ember-cli-chart.svg)](https://travis-ci.org/aomran/ember-cli-chart)
+[![Ember Observer Score](https://emberobserver.com/badges/ember-cli-chart.svg)](https://emberobserver.com/addons/ember-cli-chart)
 
 This Ember CLI addon is a simple wrapper for [ChartJS](http://www.chartjs.org/) (v2.8.0).