Make Jerome Petazzoni a maintainer for dind

In the spirit of getting more contributors to maintain their
components.. I nominate @jpetazzo ot maintain dind (he's the original
author).

@jpetazzo I don't expect this to be too much load, but it's a good and
symbolic start :)

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)