Vulkan examples, although part of the Qt GUI documentation project,
live under their own directory under /examples. Mark the correct
install path for these using the \meta command.
Fixes: QTBUG-81360
Change-Id: I0b98a19bf56d5b1953dbd90c0d5103be9041689a
Reviewed-by: Paul Wicking <paul.wicking@qt.io>