To add a note to a release (like an individual feature, upgrade, or a bug fix), first open up the release that you want to add the note to.

Once on the release management screen, you'll be shown three areas to add your notes, one each for features / upgrades / bugfixes.

Enter in the details for the note, and either click on the 'Add feature' button, or just click enter and keep typing to add another feature.

When adding your notes, if you want to add in some formatting you can use markdown.