Docs: document commit messages guidelines
Problem to solve
Document the commit messages guidelines. Introduced by https://gitlab.com/gitlab-org/gitlab-ce/issues/50003.
Further details
We have the danger bot making our pipelines fail, so we have to rebase to amend the commit, then force push. This is kinda extreme. We need to document exactly how the commit message should be written to avoid this and prevent failures.
Proposal
Add a new section ## Commit messages guidelines
into the development docs.