chore: update Twitter url to X

Author: lucaslarroche

README.md

@@ -11,7 +11,7 @@
 [![Github release](https://img.shields.io/github/v/release/picocss/pico?color=0172ad&logo=github&logoColor=white)](https://github.com/picocss/pico/releases/latest)
 [![npm version](https://img.shields.io/npm/v/@picocss/pico?color=0172ad)](https://www.npmjs.com/package/@picocss/pico)
 [![License](https://img.shields.io/badge/license-MIT-%230172ad)](https://github.com/picocss/pico/blob/master/LICENSE.md)
-[![Twitter URL](https://img.shields.io/twitter/url/https/twitter.com/picocss.svg?style=social&label=Follow%20%40picocss)](https://twitter.com/picocss)
+[![X (formerly Twitter)](https://img.shields.io/twitter/url/https/twitter.com/picocss.svg?style=social&label=Follow%20%40picocss)](https://x.com/picocss)
 
 ## Minimal CSS Framework for Semantic HTML