将readme中的demo示例改为网站链接

Signed-off-by: Nli-yan339 <liyan339@h-partners.com>

zh-cn/device-dev/Readme-CN.md

@@ -51,7 +51,7 @@
   - [Docker编译环境](get-code/gettools-acquire.md)
   - [IDE集成开发环境](get-code/gettools-ide.md)
 - 示例教程	
-  - [Demo示例](device-demo.md)
+  - [Demo示例](https://growing.openharmony.cn/mainPlay/sample)
   - [Codelabs](https://gitee.com/openharmony/codelabs/blob/master/README.md)  
 - 参考
   - [常见问题-设备开发](faqs/Readme-CN.md)