add known user

README.md

@@ -209,3 +209,4 @@ The project is licensed under the [Apache 2 license](https://github.com/ctripcor
 ![亿投传媒](https://raw.githubusercontent.com/ctripcorp/apollo/master/doc/images/known-users/reachmedia.png) 
 ![股先生](https://raw.githubusercontent.com/ctripcorp/apollo/master/doc/images/known-users/guxiansheng.png) 
 ![财学堂](https://raw.githubusercontent.com/ctripcorp/apollo/master/doc/images/known-users/caixuetang.png) 
+![4399](https://raw.githubusercontent.com/ctripcorp/apollo/master/doc/images/known-users/4399.png)