Stop restarting acpid when installing

The user will probably not expect a makefile to restart a system service when installing.  This commit removes this from the makefile and adds a note in the README for the user to restart `acpid` manually.

The other reason why it would be nice to remove this is that running `service acpid restart` does not work on Arch Linux.  The analogous command is `systemctl restart acpid`.  Some other systemd-based distributions, such as Fedora, have added a `service` compatibility command to make the old syntax work, but this is not part of systemd itself and as a result is not part of Arch Linux.

See this thread on the Arch Linux forums for more info: [How to restart services compatibly with SysVinit](https://bbs.archlinux.org/viewtopic.php?id=170989)