Ensure we remember things we should pre-announce

We removed support for Windows 7 (because we upgraded Electron) and we didn't warn users.

We'd like to do better. We think if we write some small automation that means if we create an issue with a label e.g. X-Include-In-Release-Notes we could automatically add the issue's title to every release's release notes.

This would probably involved a relatively simple update to the [allchange](https://github.com/matrix-org/allchange) script.

This might be a good thing to include in the Saner Releases epic

Start by reading the allchange script linked in the issue and checking how release notes are currently assembled. Trace how issue labels and titles could flow into each release, then verify that an issue labeled X-Include-In-Release-Notes appears in the generated release notes without affecting other issues. Consider the Saner Releases epic for surrounding context.

Written by the indexing model from the issue text.