docs: add npmx link

Author: phaux

README.md

@@ -1,6 +1,7 @@
 # React Simple FLIP
 
 [![npm](https://img.shields.io/npm/v/react-simple-flip)](https://www.npmjs.com/package/react-simple-flip)
+[![npmx](https://npmx.dev/api/registry/badge/version/react-simple-flip?label=npmx)](https://npmx.dev/package/react-simple-flip)
 [![Bundlephobia](https://img.shields.io/bundlephobia/minzip/react-simple-flip)](https://bundlephobia.com/package/react-simple-flip)
 [![jsDocs.io](https://img.shields.io/badge/jsDocs.io-reference-blue)](https://www.jsdocs.io/package/react-simple-flip)
 [![Stackblitz](https://developer.stackblitz.com/img/open_in_stackblitz_small.svg)](https://stackblitz.com/github/phaux/react-simple-flip?file=app/TodoList.tsx)