A badge to track "commits since"

[nathanjmcdougall]

Motivation
I noticed this badge on pytest-cov's README:

.. |commits-since| image:: https://img.shields.io/github/commits-since/pytest-dev/pytest-cov/v6.0.0.svg
    :alt: Commits since latest release
    :target: https://github.com/pytest-dev/pytest-cov/compare/v6.0.0...master

I think that's quite useful to see when it might be time to consider a release.

Summary of desired enhancement
Consider adding an equivalent of this badge for this project.

[nathanjmcdougall]

I'm not going to do this (for now), because it would require manually maintaining the tagged version in the markdown.

There's an equivalent badge but it requires using GitHub releases - which I'm not using currently.
https://shields.io/badges/git-hub-commits-since-latest-release

[nathanjmcdougall]

Blocked until #237