D6604: add a metainfo.yaml to make ECM a proper framework

[David Faure]

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

REPOSITORY
  R240 Extra CMake Modules

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D6604

To: sitter, ochurlaud, dfaure, skelly
Cc: #frameworks, #build_system