[TASK] Improve Documentation

UPGRADE.md

@@ -3,6 +3,8 @@
 `vimeoLightbox.js` (deprecated since 1.1.0) using magnific-popup and jQuery removed in favor of `sgVimeoLightbox.js` (vanilla JS).
 Extension project_theme_lightbox required starting with version 2.0.0.
 
+- Dropped TYPO3 9 Support
+
 ## Version 1.1  ```project_theme_lightbox``` integration
 - The magnific popup integration is deprecated and will be removed in later versions.
 - Implement JavaScript according to the readme after integrating ```project_theme_lightbox```