Update README to remove experimental notice

Removed warning about the package being experimental.

Author: smnandre

README.md

@@ -10,11 +10,6 @@
 
 # Playwright PHP - Performance
 
-> [!IMPORTANT]  
-> This package is **experimental**. Its API may still change before the upcoming `1.0` release.  
->  
-> Curious or interested? Try it out, [share your feedback](https://github.com/playwright-php/performance/issues), or ideas!
-
 The Performance package helps you inspect how a page behaves in a real browser 
 by extracting Core Web Vitals and network timing data with a single API.