Automated release process

[simonw]

Need to figure out the npm equivalent of the pattern I use for publishing my Python packages to PyPI when I create a new release tag on GitHub: https://github.com/simonw/datasette-redirect-to-https/blob/main/.github/workflows/publish.yml

In addition to publishing to npm, it should also run the build_demos.py script in the docs/ folder that I added in #1 and commit any changes back to GitHub using this pattern: https://til.simonwillison.net/github-actions/commit-if-file-changed