Add FAQ entry how to properly add package from github.

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>