Add echarts-gl in README

Author: pissang

README.md

@@ -11,8 +11,17 @@ ECharts is a free, powerful charting and visualization library offering an easy
 ## Get ECharts
 
 + Download on [echarts.baidu.com](http://echarts.baidu.com/download.html)
+
 + `npm install echarts --save`
 
+## Get ECharts GL
+
+ECharts-GL is an extension pack of echarts, which providing 3D plots, globe visualization and WebGL acceleration.
+
++ Get from [https://github.com/ecomfe/echarts-gl](https://github.com/ecomfe/echarts-gl)
+
++ `npm install echarts-gl --save`
+
 ## Docs
 
 + [Tutorial](http://echarts.baidu.com/tutorial.html)
@@ -29,6 +38,7 @@ ECharts is a free, powerful charting and visualization library offering an easy
 
 ## Resources
 
+
 ### Awesome ECharts
 
 [https://github.com/ecomfe/awesome-echarts](https://github.com/ecomfe/awesome-echarts)