misc: add readonly notice

Author: yangshun

README.md

@@ -1,8 +1,14 @@
-2048-python
+2048 Python
 ===========
 
 [![Run on Repl.it](https://repl.it/badge/github/yangshun/2048-python)](https://repl.it/github/yangshun/2048-python)
 
+---
+
+**⚠️NOTE⚠️**: We won't be accepting any contributions/changes to the project anymore. It is now readonly.
+
+---
+
 Based on the popular game [2048](https://github.com/gabrielecirulli/2048) by Gabriele Cirulli. The game's objective is to slide numbered tiles on a grid to combine them to create a tile with the number 2048. Here is a Python version that uses TKinter! 
 
 ![screenshot](img/screenshot.png)