[fix]:解决colcon代码github访问问题

docs/chapt3/3.3ROS2的编译器Colcon.md

@@ -45,9 +45,11 @@ sudo apt-get install python3-colcon-common-extensions
 2. 下载个ROS2示例源码测试一下
 
    ```
-   git clone https://github.com/ros2/examples src/examples -b foxy
+   git clone https://ghproxy.com/https://github.com/ros2/examples src/examples -b foxy
    ```
 
+> 源码在github上，https://ghproxy.com/为github代理
+
 3. 编译工程
 
    ```