Bug fixes and performance improvements
I get that we're doing the whole automated releases of whatever's passing tests and all, but release notes are important. People should be able to know what's changing in your software.
Make a process for building those notes and include them. Keep a Changelog seems to have a pretty good approach:
Don't merge in changes without updating the changelog as appropriate. Enforce this, either with code checks or with code review. If you do this, your release notes are already assembled when it's time to release.
There's not much excuse for saying "bug fixes and performance improvements." Tell us what's actually happening.