News feeds allow you to see when websites have added new content. You can get the latest updates in one place, as soon as it's published, without having to visit the websites you have taken the feed from.
Feeds are generally known as RSS (Really Simple Syndication) which are just web pages, designed to be read by computers rather than people.
Xiaomi Firmware Updater provides feeds for new firmware releases, new blog posts. While MIUI Updates Tracker provides feeds for new MIUI ROMs updates.