Release information

update documentation

build documentation cd docs_builder, pip install -r requirements-docs.txt and make html

make release

update release notes in release-notes with commit
make sure all tests run (tox -p)
bump version (bumpversion [major|minor|patch])
git push --tags (triggers release)
test installation in virtualenv from pypi

mkvirtualenv test --python=python3.9
(test) pip install sbmlutils