Add openhub badge

Author: hazendaz

README.md

@@ -6,6 +6,7 @@ MyBatis SQL Mapper Framework for Java
 [![Dependency Status](https://www.versioneye.com/user/projects/56199c04a193340f320005d3/badge.svg?style=flat)](https://www.versioneye.com/user/projects/56199c04a193340f320005d3)
 [![Maven central](https://maven-badges.herokuapp.com/maven-central/org.mybatis/mybatis/badge.svg)](https://maven-badges.herokuapp.com/maven-central/org.mybatis/mybatis)
 [![Apache 2](http://img.shields.io/badge/license-Apache%202-red.svg)](http://www.apache.org/licenses/LICENSE-2.0)
+[![Project Stats](https://www.openhub.net/p/mybatis/widgets/project_thin_badge.gif)](https://www.openhub.net/p/mybatis)
 
 ![mybatis](http://mybatis.github.io/images/mybatis-logo.png)