Add current release process to the new README.md
@vyaklushin mentioned at !1173 (comment 2116656426):
note (non-blocking): Should we also describe the current release process in README.md? Something like gitlab-com/create-stage/source-code-be#220 (comment 2111571093).
Which I think is a great idea
Related: Expand the README.md with more details (#800 - closed)