Clarify how to trigger rebuild of packages in case of last minute changes

The effect is the same as removing rebuild="local", but
it removes doubt about default OBS behavior.

See: https://openbuildservice.org/help/manuals/obs-user-guide/cha-obs-build-scheduling-and-dispatching#id-1.2.10.14.5.7



Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>