Add RELEASE.md

[dkropachev]

Add a doc that describes release proccess

Pre-review checklist

• [x] I have split my patch into logically separate commits.
• [x] All commit messages clearly explain what they change and why.
• [ ] ~~I added relevant tests for new features and bug fixes.~~
• [x] All commits compile, pass static checks and pass test.
• [x] PR description sums up the changes and reasons why they should be introduced.
• [ ] ~~I have provided docstrings for the public items that I want to introduce.~~
• [ ] ~~I have adjusted the documentation in ./docs/source/.~~
• [ ] ~~I added appropriate Fixes: annotations to PR description.~~