Briefly describe the 'arch' and 'nodump' flags.

usr.bin/chflags/chflags.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: chflags.1,v 1.28 2023/05/19 19:50:59 uwe Exp $
+.\"	$NetBSD: chflags.1,v 1.29 2023/05/24 22:33:17 jschauma Exp $
 .\"
 .\" Copyright (c) 1989, 1990, 1993, 1994
 .\"	The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"	@(#)chflags.1	8.4 (Berkeley) 5/2/95
 .\"
-.Dd May 19, 2023
+.Dd May 24, 2023
 .Dt CHFLAGS 1
 .Os
 .Sh NAME
@@ -104,6 +104,18 @@ The following keywords are currently defined:
 .It Li uchg Ta user immutable Ta owner or super-user
 .El
 .Pp
+The
+.Va arch
+flag is only used in connection with certain foreign
+filesystems (e.g., MS-DOS, where it indicates whether
+a file has been modified since it was last backed up).
+.Pp
+A file with the
+.Va nodump
+flag set will by default only be backed up by
+.Xr dump 8
+during full backups.
+.Pp
 Putting the letters
 .Sq Cm no
 before a keyword causes the flag to be turned off.