update README.md.

README.md

@@ -93,14 +93,9 @@
   * [安装Python环境](references_tips/InstallPython.md)
   * [Python tips](references_tips/python)
 
-* Git
-  * [Git Tips - 常用方法速查，快速入门](https://gitee.com/pi-lab/learn_programming/blob/master/6_tools/git/README.md)
-  * [Git快速入门 - Git初体验](https://my.oschina.net/dxqr/blog/134811)
-  * [在win7系统下使用TortoiseGit(乌龟git)简单操作Git](https://my.oschina.net/longxuu/blog/141699)
-  * [Git系统学习 - 廖雪峰的Git教程](https://www.liaoxuefeng.com/wiki/0013739516305929606dd18361248578c67b8067c8c017b000)
-
-* Markdown
-  * [Markdown—入门指南](https://www.jianshu.com/p/1e402922ee32)
+* [Git教程](https://gitee.com/pi-lab/learn_programming/blob/master/6_tools/git/README.md)
+* [Markdown教程](https://gitee.com/pi-lab/learn_programming/blob/master/6_tools/markdown/README.md)
+