Fix mentioned distributions within the setup tutorial
Fix mentioned distributions within the setup tutorial

Currently, the PPA from project atomic only works on Ubuntu. We should
only mention that distribution there otherwise it won't work.

Signed-off-by: Sascha Grunert <70ab469ddb2ac3e35f32ed7c2fd1cca514b2e879@suse.com>

mikebrow/cri-o,mikebrow/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o,nalind/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid