link to release notes on update page
On the system update page where it lists the current version, new version, and the "confirm" button, there should be a link (or the actual text inside a folded section) to the release notes for that update.
In the case of multiple updates, all notes between then and now should be shown.
I have another appliance for my phone system and it does this by linking to a dynamic page with the old/new version numbers and they display all the notes in that page.
Barring that, even just a link to the release notes index page would be a great reminder to read those before applying the updates.