chore: update readme

Author: sudo-tee

README.md

@@ -12,6 +12,8 @@
 [![GitHub stars](https://img.shields.io/github/stars/sudo-tee/opencode.nvim?style=for-the-badge)](https://github.com/sudo-tee/opencode.nvim/stargazers)
 ![Last Commit](https://img.shields.io/github/last-commit/sudo-tee/opencode.nvim?style=for-the-badge)
 
+<a href="https://www.buymeacoffee.com/sudo.tee"><img src="https://www.buymeacoffee.com/assets/img/custom_images/orange_img.png" height="20px"></a>
+
 </div>
 
 ## ✨ Description