* Minor update to Readme - Statemint section

Common good -> System

* update parchains readme

* Update parachains/README.md

Co-authored-by: Bastian Köcher <git@kchr.de>

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Bastian Köcher <git@kchr.de>