TL: bump version to 5.5.2 + added release guide for maintainers (#489)

* TL: added release guide

* TL: additional detail

* Update 07_release_guide.md

* TL: minor correction on release guide

* TL: typo

* TL: lighter testing

* TL: bump version to 5.5.2

* TL: let's not care

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Co-authored-by: Robert Speck <pancetta@users.noreply.github.com>