add the architecture extend png.

README.md

@@ -28,7 +28,7 @@ Apache License, Version 2.0
 
 Both extension module and layered project architecture is according to Apache Dubbo (including protocol layer, registry layer, cluster layer, config layer and so on), the advantage of this arch is as following: you can implement these layered interfaces in your own way, override the default implementation of dubbo-go by calling 'extension.SetXXX' of extension, complete your special needs without modifying the source code. At the same time, you are welcome to contribute implementation of useful extension to the community.
 
-![frame design](https://raw.githubusercontent.com/wiki/dubbo/dubbo-go/dubbo-go%E4%BB%A3%E7%A0%81%E5%88%86%E5%B1%82%E8%AE%BE%E8%AE%A1.png)
+![dubbo go extend](./doc/pic/arch/dubbo-go-ext.png)
 
 If you wanna know more about dubbo-go, please visit this reference [Project Architeture design](https://github.com/apache/dubbo-go/wiki/dubbo-go-V1.0-design)
 

README_CN.md

@@ -27,7 +27,7 @@ Apache License, Version 2.0
 
 基于dubbo的extension模块和分层的代码设计(包括 protocol layer, registry layer, cluster layer, config 等等)。我们的目标是：你可以对这些分层接口进行新的实现，并通过调用 extension 模块的“ extension.SetXXX ”方法来覆盖 dubbo-go [同 go-for-apache-dubbo ]的默认实现，以完成自己的特殊需求而无需修改源代码。同时，欢迎你为社区贡献有用的拓展实现。
 
-![框架设计](https://raw.githubusercontent.com/wiki/dubbo/dubbo-go/dubbo-go%E4%BB%A3%E7%A0%81%E5%88%86%E5%B1%82%E8%AE%BE%E8%AE%A1.png)
+![dubbo go extend](./doc/pic/arch/dubbo-go-ext.png)
 
 关于详细设计请阅读 [code layered design](https://github.com/apache/dubbo-go/wiki/dubbo-go-V1.0-design)