doc: update readme (#4589)

Add contribution leaderboard badge into README file.

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

README.md

@@ -4,6 +4,7 @@
 ![license](https://img.shields.io/github/license/alibaba/canal.svg)
 [![average time to resolve an issue](http://isitmaintained.com/badge/resolution/alibaba/canal.svg)](http://isitmaintained.com/project/alibaba/canal "average time to resolve an issue")
 [![percentage of issues still open](http://isitmaintained.com/badge/open/alibaba/canal.svg)](http://isitmaintained.com/project/alibaba/canal "percentage of issues still open")
+[![Leaderboard](https://img.shields.io/badge/Canal-%E6%9F%A5%E7%9C%8B%E8%B4%A1%E7%8C%AE%E6%8E%92%E8%A1%8C%E6%A6%9C-orange)](https://opensource.alibaba.com/contribution_leaderboard/details?projectValue=canal)
 
 ## 简介