Explain the 's' image size better.

usr.sbin/makefs/makefs.8

@@ -1,4 +1,4 @@
-.\"	$NetBSD: makefs.8,v 1.61 2017/02/12 14:45:09 wiz Exp $
+.\"	$NetBSD: makefs.8,v 1.62 2017/04/13 17:21:29 christos Exp $
 .\"
 .\" Copyright (c) 2001-2003 Wasabi Systems, Inc.
 .\" All rights reserved.
@@ -33,7 +33,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd February 11, 2017
+.Dd April 13, 2017
 .Dt MAKEFS 8
 .Os
 .Sh NAME
@@ -200,6 +200,19 @@ Defaults to 512.
 .It Fl s Ar image-size
 Set the size of the file system image to
 .Ar image-size .
+This is equivalent of setting both the minimum
+.Fl ( m )
+and the maximum
+.Fl ( M )
+sizes to
+.Ar image-size.
+For 
+.Sy ffs
+and
+.Sy msdos
+the
+.Ar offset
+is not included on that size.
 .It Fl T Ar timestamp
 Specify a timestamp to be set for all file system files and directories
 created so that repeatable builds are possible.