Instructions for installing on fedora 20

A start on the documentation parts of: https://clusterhq.atlassian.net/browse/FLOC-957
We need the kernel-devel package for the currently running kernel (at least for the zpool command that follows below). And, unfortunately, that kernel is often not in the upstream repository anymore, and varies across providers.

It would be better to suggest upgrading to the latest kernel but, anecdotally, I've had issues trying to upgrade the kernel. It would also require a reboot.