D7681: Update human-readable tier designation in API dox

[David Faure]

dfaure accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R169 Kirigami

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D7681

To: adridg, dfaure, mart
Cc: plasma-devel, apol, mart, hein