Basic markdown and Sphinx to build into HTML, publishing via github pages. It's an open source project so putting the docs alongside the code just makes sense. Although Sphinx isn't great for my money, it gets the job done.
sphinx-build docs docs/html
git branch -D gh-pages || true
git checkout -B gh-pages-stage
touch docs/html/.nojekyll
git add --force docs/html
git commit -m "Docs"
git push --force origin $(git subtree split --prefix docs/html --branch gh-pages):refs/heads/gh-pages
git checkout -