UPGRADE.md

## Version 5
- `youtubeLightbox.js` (deprecated since 4.4.0) using magnific-popup and jQuery removed in favor of `sgYoutubeLightbox.js` (vanilla JS).
- Extension `project_theme_lightbox` required starting with version 5.0.0.
- Dropped TYPO3 9 Support

## Version 4.4  ```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```

## Version 4 Breaking Changes

- Dropped TYPO3 8 support