How can I get notified once my device is supported?
https://lineageos.org/feed.xml
A site called LineageOS Changelog tracks device support, but you'll have to check manually:
You can also find the XDA Developers forum for your device, and follow the LineageOS thread for updates:
https://forum.xda-developers.com/
Finally, for real-time updates, you can view the commits to the LineageOS repositories themselves:
https://www.reddit.com/r/LineageOS/comments/9ulb17/is_there_...
https://www.reddit.com/r/LineageOS/comments/an1fo9/whats_hol...
The LineageOS subreddit is another news source, as development team members do comment there.