Add online books about C programming (#11077)

* Add online books about C programming

Signed-off-by: xiaobo <xiaobo@uniontech.com>

* Update free-programming-books-zh.md

---------

Signed-off-by: xiaobo <xiaobo@uniontech.com>

books/free-programming-books-zh.md

@@ -314,6 +314,7 @@
 * [新概念 C 语言教程](https://github.com/limingth/NCCL)
 * [Beej's Guide to Network Programming 簡體中文版](https://beej-zhtw-gitbook.netdpi.net) - Brian "Beej Jorgensen" Hall, 廖亚伦译
 * [C 语言常见问题集](http://c-faq-chn.sourceforge.net/ccfaq/ccfaq.html)
+* [C 语言入门教程](https://www.dotcpp.com/course/c/)
 * [Linux C 编程一站式学习](https://web.archive.org/web/20210514225440/http://docs.linuxtone.org/ebooks/C&CPP/c/) *(:card_file_box: archived)*