docs: add deno badge to show supported version

Author: lambdalisue

README.md

@@ -1,6 +1,7 @@
 # 🍂 fall-core
 
 [![JSR](https://jsr.io/badges/@vim-fall/core)](https://jsr.io/@vim-fall/core)
+[![Deno](https://img.shields.io/badge/Deno%202.x-333?logo=deno&logoColor=fff)](#)
 [![Test](https://github.com/vim-fall/fall-core/actions/workflows/test.yml/badge.svg)](https://github.com/vim-fall/fall-core/actions/workflows/test.yml)
 [![MIT License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)