add invidious as alternative YouTube frontend

additionally offer an alternative youtube frontend

install with docker https://github.com/iv-org/invidious

Audio-only mode (and no need to keep window open on mobile)
Lightweight (the homepage is ~4 KB compressed)
Tools for managing subscriptions:
Only show unseen videos
Only show latest (or latest unseen) video from each channel
Delivers notifications from all subscribed channels
Automatically redirect homepage to feed
Import subscriptions from YouTube
Dark mode
Embed support
Set default player options (speed, quality, autoplay, loop)
Support for Reddit comments in place of YouTube comments
Import/Export subscriptions, watch history, preferences

documentation https://github.com/iv-org/documentation