Reword post mortem description. It tries to get the tree averages if …

…it can.

lib/libkvm/kvm_getloadavg.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: kvm_getloadavg.3,v 1.12 2018/12/11 02:29:11 sevan Exp $
+.\"	$NetBSD: kvm_getloadavg.3,v 1.13 2018/12/11 23:02:19 sevan Exp $
 .\"
 .\" Copyright (c) 1992, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -58,8 +58,8 @@ On a live system, the load average is obtained by calling
 .Xr getloadavg 3 .
 If performing post mortem on a kernel core file,
 .Nm
-obtains the system load average at the time of death from the core file
-directly.
+is able to extract the system load averages at the time of death from the core
+file directly.
 .Sh RETURN VALUES
 If the load average was unobtainable, \-1 is returned; otherwise,
 the number of samples actually retrieved is returned.