Document the mounts.conf file
Document the mounts.conf file

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #521
Approved by: rhatdan

projectatomic/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,nalind/buildah-1,rhatdan/buildah,nalind/buildah,projectatomic/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,nalind/buildah-1,nalind/buildah-1,ipbabble/buildah,ipbabble/buildah,rhatdan/buildah,nalind/buildah,TomSweeneyRedHat/buildah