media: docs: add GPLv2 for uAPI guide

Newer uAPI docs should be dual-licensed with both GPL
and GFDL. Add a text adding the GPLv2 license text there,
in order to be coherent with the included docs.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
1 file changed