Recent releases don't have corresponding tags on GitHub

[tesujimath]

Excited to see these new releases, and asking nicely if you could continue to push corresponding tags to GitHub, as per #116

Thanks!

[tesujimath]

Actually I have switched my Nix package fetcher to fetch from PyPI rather than GitHub, and since that works fine provided there's a source tarball on PyPI, I can live without GitHub tagging. But I still think it's a good idea. 😉