Add Star History chart

Is your feature request related to a problem? Please describe.

There's no problem this solves, it's a gimmick that's perhaps cool.

Describe the solution you'd like

https://star-history.com/ provides a chart of how many stars a GitHub project has. See here for OC. We could embed this image somewhere in the Readme or in the docs:

Describe alternatives you've considered

We could instead or also use GitHub Readme Stats (though that seems only for individual profiles, not repos) or GitHub Stats (see OC stats here).