The fix from cb263973ac was made the other way around,
i.e. `SIGKILL` was changed to `SIGUSR1`, but the sentence is about a "termination signal", i.e. `SIGKILL`, not `SIGUSR1`.
systemctl supports runlevel invocation name without utmp.
The runlevel symlink is installed unconditionally.
So it's reasonable to install runlevel manpage with it as well.
Signed-off-by: Jan Chren (rindeal) <dev.rindeal@gmail.com>