Update README.md (#133)

Update the read me to include Zetr, a tetris clone for the terminal.

Author: ajTronic

README.md

@@ -484,6 +484,7 @@ TOC is generated by [markdown-toc](https://github.com/jonschlinkert/markdown-toc
 - [DanB91/Zig-Playdate-Template](https://github.com/DanB91/Zig-Playdate-Template) : Starter code for a Playdate program written in Zig.
 - [foxnne/aftersun](https://github.com/foxnne/aftersun) : Top-down 2D RPG.
 - [4imothy/termy48](https://github.com/4imothy/termy48) : A 2048 game to run in terminal.
+- [ajTronic/zetr](https://github.com/ajTronic/zetr) : An aesthetic tetris clone for the terminal written in Zig.
 - [andrewrk/clashos](https://github.com/andrewrk/clashos) multiplayer arcade game for bare metal Raspberry Pi 3 B+.
 - [MasterQ32/Ziguana-Game-System](https://github.com/MasterQ32/Ziguana-Game-System) A retro-style gaming console running on bare x86 metal written in Zig.
 - [Srekel/zag](https://github.com/Srekel/zag) : Game dev project written in Zig and C.