Add release checklist (#1316)

* Add release checklist

* add space to checkbox

* polkadot-js-apps

* Apply suggestions from code review

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* add notes for each release item

* Apply suggestions from code review

Co-authored-by: s3krit <pugh@s3kr.it>

* Apply suggestions from code review

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: Gavin Wood <gavin@parity.io>

* Update RELEASE.md

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update RELEASE.md - rearrange sections

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: joepetrowski <joe@parity.io>
Co-authored-by: s3krit <pugh@s3kr.it>
Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: Gavin Wood <gavin@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
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