docs: add live demo badge to README

- Added link to live demo

Author: fulleni

README.md

@@ -1,6 +1,7 @@
 # 📱✨ ht_main
 
 ![coverage: percentage](https://img.shields.io/badge/coverage-XX-green)
+[![Demo: Live](https://img.shields.io/badge/Demo-Live-orange)](https://headlines-toolkit.github.io/ht-main/)
 [![style: very good analysis](https://img.shields.io/badge/style-very_good_analysis-B22C89.svg)](https://pub.dev/packages/very_good_analysis)
 [![License: PolyForm Free Trial](https://img.shields.io/badge/License-PolyForm%20Free%20Trial-blue)](https://polyformproject.org/licenses/free-trial/1.0.0)