per subcommand manpage

manpage repo: https://github.com/ipbabble/docker-man

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com> (github: lsm5)

	new file:   contrib/man/man1/docker-attach.1
	new file:   contrib/man/man1/docker-build.1
	new file:   contrib/man/man1/docker-images.1
	new file:   contrib/man/man1/docker-info.1
	new file:   contrib/man/man1/docker-rm.1
	new file:   contrib/man/man1/docker-rmi.1
	new file:   contrib/man/man1/docker-run.1
	new file:   contrib/man/man1/docker-tag.1
	new file:   contrib/man/man1/docker.1