pkg: systemd: add initial MAINTAINERS

I volunteered for pkg/systemd MAINTAINER and there were no objections
during the #docker-dev meeting. For context I wrote most of the stuff in
here and wrote the dependent calls in api.go. Plus, I actively test the
code via CoreOS.

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Merge pull request #3978 from philips/add-philips-as-pkg-systemd-maintainer

pkg: systemd: add initial MAINTAINERS
Merge pull request #3932 from SvenDowideit/no-docker-meeting-channel

remove mention of #docker-meeting
Merge pull request #3987 from SvenDowideit/warn-against-symlinks

please, for the love of Docker, do. not. use. symlinks
partial version

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
speeling

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
work in progress

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)