Updated Fedora policy github wiki page

[Miroslav Grepl]

Hi folks,
We are working on updated wiki for Fedora Policy github repository. It
should help you to contribute and work together with us.

See

https://github.com/fedora-selinux/selinux-policy/wiki/HowToContribute
https://github.com/fedora-selinux/selinux-policy/wiki/Packaging

This is still in progress and your ideas are really welcomed.

Thank you.