Document the security.bsd.unprivileged_idprio in idprio(1) in addition

to rtprio(2).

Approved by:	wblock
MFC after:	3 days

usr.sbin/rtprio/rtprio.1

@@ -30,7 +30,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 23, 1994
+.Dd September 29, 2012
 .Dt RTPRIO 1
 .Os
 .Sh NAME
@@ -113,6 +113,14 @@ highest priority
 of 0 means "the current process".
 .Pp
 Only root is allowed to set realtime or idle priority for a process.
+A user may modify the idle priority of their own processes if the
+.Xr sysctl 8
+variable
+.Va security.bsd.unprivileged_idprio
+is set to non-zero.
+Note that this increases the chance that a deadlock can occur
+if a process locks a required resource and then does
+not get to run.
 .Sh EXIT STATUS
 If
 .Nm