Release notes
The blog post on home-assistant.io that tells what is new in a release, what changed, and what users need to do about it.
The release notes go live on the Home Assistant blog on the day of the release. Next to the highlights, they have a section for every patch release, a section with the backward-incompatible changes, and a list of all changes.
The text about a backward-incompatible change comes from the description of its pull request. That is why the pull request template asks you to write it for users. See Release notes and the release party.