feat: update chapter(s) by CAT

Author: cssmagic

README.md

@@ -41,7 +41,12 @@
 	* [2.5 我们的第一个编程练习](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/35)
 	* [本章小结](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/30)
 3. [第三章 设计函数](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/27)
-	* (TBD)
+	* 3.1   [Functions](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/36)
+	* 3.2   Benefits of functions
+	* 3.3   Roles of functions
+	* 3.4   What’s a reasonable task for a function?
+	* 3.5   The cycle of design of functions with Copilot
+	* 3.6   Examples of creating good functions with Copilot
 	* [本章小结](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/28)
 4. [第四章 理解 Python 代码（上）](https://github.com/cssmagic/Learn-AI-Assisted-Python-Programming/issues/25)
 	* (本章正文略)