Revert "Revert the package signing instructions."

This reverts commit 8ca7979167553ea99df409156911fb35c22580bb.

We fixed it.
download: Fix the signing instructions. Make everything more clear.
download: Add 'pacman-key --init'.
download: Make mirror urls hyperlinks.
Merge branch 'master' of http://github.com/BlackArch/blackarch-site