Updated README for comma code

Author: itsmohitj

README.md

@@ -2,4 +2,6 @@
 This repo contains my project solutions for [Automate the Boring Stuff with Python by Al Sweigart](https://automatetheboringstuff.com/)
 
 - Chapter 3: Functions
-    - [The Collatz Sequence](https://github.com/itsmohitj/automate_the_boring_stuff_project_solutions/tree/main/The_Collatz_Sequence)
+    - [The Collatz Sequence](https://github.com/itsmohitj/automate_the_boring_stuff_project_solutions/tree/main/The_Collatz_Sequence)
+- Chapter 4: Lists
+    - [Comma Code](https://github.com/itsmohitj/automate_the_boring_stuff_project_solutions/tree/main/Comma_Code)