Update free-programming-books-zh.md

free-programming-books-zh.md

@@ -19,6 +19,7 @@
 * [Udacity](https://www.udacity.com/)
 * [xuetangX](https://www.xuetangx.com/)
 * [Codecademy](http://www.codecademy.com/?locale_code=zh)
+* [CodeSchool](https://www.codeschool.com/)
 
 
 ###软件开发方法