contrib/init/systemd: add philips as MAINTAINER

As requested after #7021 add me as a maintainer alongside the sword
toting @lsm5.

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Merge pull request #7090 from philips/add-philips-to-systemd-maintainers

contrib/init/systemd: add philips as MAINTAINER