set date to when this utility became default system sort(1) on NetBSD

add information about when it came to NetBSD to HISTORY

usr.bin/sort/sort.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: sort.1,v 1.9 2001/01/13 21:40:56 jdolecek Exp $
+.\"	$NetBSD: sort.1,v 1.10 2001/01/16 10:36:57 jdolecek Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -36,7 +36,7 @@
 .\"
 .\"     @(#)sort.1	8.1 (Berkeley) 6/6/93
 .\"
-.Dd June 6, 1993
+.Dd January 13, 2001
 .Dt SORT 1
 .Os
 .Sh NAME
@@ -363,7 +363,9 @@ command appeared in
 This
 .Nm
 implementation appeared in
-.Bx 4.4 .
+.Bx 4.4
+and is used since
+.Nx 1.6 .
 .Sh NOTES
 This
 .Nm