Clarify that this is experimental.

Change-Id: I7a83d80c0db233a48026d1254021b926f28002f3
Reviewed-on: https://gerrit.libreoffice.org/46782Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-on: https://gerrit.libreoffice.org/46937Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>