Network installation link update

[Rahul Sundaram <sundaram fedoraproject org>]

Hi


http://fedoraproject.org/get-fedora.html points to a FC6 link. Replace 
it with 
http://docs.fedoraproject.org/install-guide/f7/en_US/sn-which-files.html 
instead.

Might be worth highlighting the installation guide on the whole 
prominently in this page too.

Is anyone working on the description of spins?

Rahul