Add RELEASE.md

[consideRatio]

This is the release process as I understand it. @jacobtomlinson can you validate this to make sense?

1. Make a empty commit with message like this.

   git commit --allow-empty -m "Version 2022.11.0"
   

2. Tag the commit with an annotation and message like this.

   git tag -a 2022.11.0 -m "Version 2022.11.0"
   

3. Push the commit and tag

   git push --follow-tags --atomic
   

[jacobtomlinson]

Pretty much, I usually run this script https://github.com/dask/helm-chart/blob/main/ci/release.sh.

This used to be documented in the README, then daskhub was added and the instructions got bumped into dask/README.md, then we got rid of that README but you can still find it if you check the artifacthub page.

I propose we take the whole "Maintaining" section out of the dask chart README (which is now only captured in the .frigate template) and move it up to the top level README. I always prefer instructions like this to be at the end of the README rather than in a separate RELEASE file.