Update teaching.md

Author: chengjun

_pages/teaching.md

@@ -50,7 +50,7 @@ I am organizing the [**Tycho Reading Club**](https://search.bilibili.com/all?key
 ![image](https://user-images.githubusercontent.com/543384/147380016-da65a625-6480-47f4-8e27-5034d696f553.png)
 
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-<a href="https://github.com/SocratesClub/SocratesClub.github.io/edit/master/_pages/teaching.mdd">
+<a href="https://github.com/SocratesClub/SocratesClub.github.io/edit/master/_pages/teaching.md">
   <img src="https://user-images.githubusercontent.com/543384/192227995-fdb3a693-2f68-4dc4-b9bd-06053066322f.png" width = "800" align="middle" />
 </a>
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