cmd/skopeo: show full help on 'copy' with no args
cmd/skopeo: show full help on 'copy' with no args

Signed-off-by: Vincent Batts <d01a4772f0cffd3f005a7d7f01c59cd104c7a5fe@hashbangbash.com>

projectatomic/skopeo,mtrmac/skopeo,jwhonce/skopeo,mtrmac/skopeo,jwhonce/skopeo,projectatomic/skopeo,mtrmac/skopeo