Add release checklist (#1316)

* Add release checklist

* add space to checkbox

* polkadot-js-apps

* Apply suggestions from code review

Co-authored-by: joe petrowski <[email protected]>

* add notes for each release item

* Apply suggestions from code review

Co-authored-by: s3krit <[email protected]>

* Apply suggestions from code review

Co-authored-by: Pierre Krieger <[email protected]>
Co-authored-by: Gavin Wood <[email protected]>

* Update RELEASE.md

Co-authored-by: Bastian Köcher <[email protected]>

* Update RELEASE.md - rearrange sections

Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: joepetrowski <[email protected]>
Co-authored-by: s3krit <[email protected]>
Co-authored-by: Pierre Krieger <[email protected]>
Co-authored-by: Gavin Wood <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>