The license is referenced in various headers, so we should ship it.
The text was copied from gnulib commit d64d66cc4897d605f543257dcd0,
file doc/COPYINGv3.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Collin Funk <collin.funk1@gmail.com>
Signed-off-by: Florian Weimer <fweimer@redhat.com>