doc: update readme

Add contribution leaderboard badge into README file.

Signed-off-by: frank-zsy <syzhao1988@126.com>

README.md

@@ -8,6 +8,7 @@
 ![license](https://img.shields.io/github/license/alibaba/arthas.svg)
 [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/alibaba/arthas.svg)](http://isitmaintained.com/project/alibaba/arthas "Average time to resolve an issue")
 [![Percentage of issues still open](http://isitmaintained.com/badge/open/alibaba/arthas.svg)](http://isitmaintained.com/project/alibaba/arthas "Percentage of issues still open")
+[![Leaderboard](https://img.shields.io/badge/Arthas-Check%20Your%20Contribution-orange)](https://opensource.alibaba.com/contribution_leaderboard/details?projectValue=arthas)
 
 `Arthas` is a Java Diagnostic tool open sourced by Alibaba.