Ensure PRs get changelog entries

[python-desert]

Maybe every PR should have a changelog entry.

The difference between a commit message and a changelog entry is usually said to be that changelog entries are for users and commit messages are for maintainers. Project-management PRs don't necessarily have any user-facing information so maybe they don't need a changelog message. But they could have one anyway.

[altendky]

So towncrier? I haven't looked into alternatives.

[python-desert]

I've been using towncrier. I've faced some issues with it, and it doesn't seem to be taking contributions. There are some recent alternatives:

• https://github.com/edx/scriv
• https://github.com/jonathanj/cacofonix