Add description of read-only/read-write

Docker-DCO-1.1-Signed-off-by: Daniel Walsh <dwalsh@redhat.com> (github: rhatdan)
Add restorecon/matchpathcon/chcon so we can label content on the fly

Docker-DCO-1.1-Signed-off-by: Daniel Walsh <dwalsh@redhat.com> (github: rhatdan)
Automatically relabel volume mounts if user passes :Z on -v command

Docker-DCO-1.1-Signed-off-by: Daniel Walsh <dwalsh@redhat.com> (github: rhatdan)