added systemd service file

just put msm.service in /etc/systemd/system/ and make sure you have msm
accessible via /usr/local/bin

enable:  systemctl enable msm.service
disable: systemctl disable msm.service
start:   systemctl start msm.service
stop:    systemctl stop msm.service
added installer for arch linux
Merge pull request #217 from FSMaxB/master

Added support for systemd and Arch Linux