docs: add npm version badge

Author: tahmarrrr23

README.md

@@ -4,6 +4,7 @@
 
 ---
 
+[![npm version](https://badgen.net/npm/v/@lycorp-jp/tappy)](https://www.npmjs.com/package/@lycorp-jp/tappy)
 [![Github Action](https://github.com/yahoojapan/tappy/actions/workflows/ci.yml/badge.svg)](https://github.com/yahoojapan/tappy/actions/workflows/ci.yml)
 
 Tappy analyzes the size of buttons, links, and other interactive elements on smartphone web screens and displays tap success rates.