* gnu/services/desktop.scm (bool): New top-level helper.
  (upower-configuration-file): Use top-level `bool'.
  (geoclue-application): New public function.
  (%standard-geoclue-applications): New public variable.
  (geoclue-service): New public variable.
  (%desktop-services): Add GeoClue.  Add a comment about activation.
* doc/guix.texi (Desktop Services): Document the GeoClue service.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>