add wechat link (#352)

add joinus

README.md

@@ -37,7 +37,9 @@ PaddleClas is a toolset for image classification tasks prepared for the industry
 
 * Scan the QR code below with your Wechat, you can access to official technical exchange group. Look forward to your participation.
 
-![](docs/images/joinus.png)
+<div align="center">
+<img src="./docs/images/joinus.png"  width = "200" height = "200" />
+</div>
 
 ## Tutorials
 

README_cn.md

@@ -41,7 +41,9 @@
 
 * 微信扫描二维码加入官方交流群，获得更高效的问题答疑，与各行各业开发者充分交流，期待您的加入。
 
-![](docs/images/joinus.png)
+<div align="center">
+<img src="./docs/images/joinus.png"  width = "200" height = "200" />
+</div>
 
 
 ## 文档教程