Appdata: Add copyright information

See https://blogs.gnome.org/hughsie/2013/10/01/copyright-in-appdata-files/ for details.
3 jobs for master in 3 minutes and 4 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #14533
run-appdata

00:00:05

passed #14532
run-tests

00:02:48

 
  Build
passed #14534
run-build

00:00:10