[Rdo-list] Quickstart should mention architecture requirements

I just spent some time debugging an issue on #rdo in which someone appeared to have done everything correctly but was unable to install RDO because of several missing packages. It turns out this was because they were working with an i686 CentOS image. I think we need to update the "Prerequisites" section of the Quickstart document (http://openstack.redhat.com/Quickstart) to indicate that we only support x86_64, because otherwise this is a tricky failure mode to detect: there are no particular errors, and all the .noarch packages still show up, so the problem is not immediately obvious. -- Lars Kellogg-Stedman <lars(a)redhat.com&gt; | larsks @ irc Cloud Engineering / OpenStack | " " @ twitter