Currently, versions in README.md need to be manually updated, and we
check it's done with a bash script.
Add a small utility playbook to add versions in README.md from their
actual default values, automatically.
This is done in pre-commit, and replace the scripted check ; instead it
will autofix the README.md, and fails in CI if needed.
We switch markdownlint behind the local hooks to gave it the opportunity
to catch a problem with the rendering.
