These guidelines are meant to be a simple, effective way to quickly discern the type of contribution in our projects, as well as an attempt to enforce limiting commits to a single topic and avoid unwieldy commits
It's based on Angular's contribution guidelines, and this document about commit messages in general. I suggest that you give them a read, too.
A commit message consists of, at the very least, the summary. It may also include a body, separated from the summary by a blank line.