test: Update and organize README
test: Update and organize README

Document the alternate runtime selection when running integratiom
tests on the host, and at the same time rganize the file a little
better.

Signed-off-by: Samuel Ortiz <0ba86cb3f08bbb861958e54bd3438887adb4263c@linux.intel.com>

umohnani8/cri-o,intelsdi-x/cri-o,rhatdan/cri-o,sameo/cri-o,jawnsy/cri-o,14rcole/cri-o,apilloud/cri-o,nalind/cri-o,rhatdan/cri-o,mikebrow/cri-o,mikebrow/cri-o,apilloud/cri-o,vbatts/cri-o,14rcole/cri-o,intelsdi-x/cri-o,umohnani8/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,jawnsy/cri-o,apilloud/cri-o,aweiteka/cri-o,jwhonce/ocid,rhatdan/cri-o,jwhonce/ocid,jwhonce/ocid,mheon/cri-o,14rcole/cri-o,jawnsy/cri-o,kubernetes-incubator/cri-o,mheon/cri-o,kubernetes-incubator/ocid,sameo/cri-o,umohnani8/cri-o,mikebrow/cri-o,nalind/cri-o,mheon/cri-o,14rcole/cri-o,aweiteka/cri-o,mikebrow/cri-o,umohnani8/cri-o,vbatts/cri-o,vbatts/cri-o,nalind/cri-o,intelsdi-x/cri-o,vbatts/cri-o,kubernetes-incubator/cri-o,rhatdan/cri-o,aweiteka/cri-o,mheon/cri-o,kubernetes-incubator/ocid,sameo/cri-o