Add BrowserStack to README.md

Author: schlagmichdoch

README.md

@@ -110,6 +110,7 @@ Connect to others in complex network situations, or over the Internet.
 * [NoSleep](https://github.com/richtr/NoSleep.js) display sleep, add wake lock ([MIT](licenses/MIT-NoSleep))
 * [heic2any](https://github.com/alexcorvi/heic2any) HEIC/HEIF to PNG/GIF/JPEG ([MIT](licenses/MIT-heic2any))
 * [Weblate](https://weblate.org/) web-based localization tool
+* [BrowserStack](https://www.browserstack.com/) This project is tested with BrowserStack
 
 [FAQ](docs/faq.md)