docs: add new feature descriptions to README}
- Add desktop notifications feature with OS-level toast support - Add auto language detection for 30 supported translations - Add auto-launch on login option for AppImage, deb, and rpm - Add settings backup/restore (export/import as JSON) - Add offline detection and auto-reload documentation - Add report issue / request feature menu item entry - Add duplicate tab option to tab context menu table - Note Snap availability for amd64 and arm64 architectures - Add unit tests (Vitest) and GitHub mirror notes to development section