[ticket/12316] Add Build Status Icon for develop-ascraeus to README.md

PHPBB3-12316
Merge remote-tracking branch 'VSEphpbb/ticket/12316' into develop-olympus

* VSEphpbb/ticket/12316:
  [ticket/12316] Add Build Status Icon for develop-ascraeus to README.md
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus:
  [ticket/12316] Add Build Status Icon for develop-ascraeus to README.md