Add Filament 4 beta caution to readme

Author: MarcelWeidum

README.md

@@ -7,6 +7,9 @@
 This package offers a straightforward and easy-to-use alert component for your Filament application. It allows you to quickly implement customizable alert messages, enhancing the user experience by
 providing clear and concise notifications.
 
+> [!CAUTION]
+> **Filament 4** is currently in beta — use it cautiously in production.
+
 ![Simple Alert](https://github.com/CodeWithDennis/filament-simple-alert/raw/4.x/resources/screenshots/thumbnail.png)
 
 ## Installation