- Remove redundant argument to (successive) `.Nm' macro;

- copy exact line from root's crontab(5) file (and the user name
  is indeed unneeded, as root's crontab(5) file is not the system's
  one);
- reword the warning: cron(8) _is_ running, by default.

From patch by Bug Hunting.

While here, remove xref to itself.

libexec/atrun/atrun.8

@@ -1,4 +1,4 @@
-.\" $NetBSD: atrun.8,v 1.11 2002/01/15 02:19:26 wiz Exp $
+.\" $NetBSD: atrun.8,v 1.12 2012/06/20 09:43:51 wiz Exp $
 .\" $OpenBSD: atrun.8,v 1.4 1998/05/22 22:16:29 deraadt Exp $
 .\" $FreeBSD: atrun.man,v 1.3 1997/02/22 14:20:55 peter Exp $
 .Dd April 12, 1995
@@ -8,7 +8,7 @@
 .Nm atrun
 .Nd run jobs queued for later execution
 .Sh SYNOPSIS
-.Nm atrun
+.Nm
 .Op Fl l Ar load_avg
 .Op Fl d
 .Sh DESCRIPTION
@@ -19,11 +19,11 @@ Root's
 .Xr crontab 5
 must contain the line:
 .Bd -literal
-*/10     *       *       *       *       root    /usr/libexec/atrun
+*/10	*	*	*	*	/usr/libexec/atrun
 .Ed
 .Pp
 so that
-.Xr atrun 8
+.Nm
 gets called every ten minutes.
 .Pp
 At every invocation, every job in lowercase queues whose starting time
@@ -44,9 +44,9 @@ Debug; print error messages to standard error instead of using
 .Sh WARNINGS
 For
 .Nm
-to work, you have to start up a
+to work, a
 .Xr cron 8
-daemon.
+daemon needs to be running.
 .Sh FILES
 .Bl -tag -width /var/at/spool -compact
 .It Pa /var/at/spool