mount_9p(8): document the new -C option.

usr.sbin/puffs/mount_9p/mount_9p.8

@@ -1,4 +1,4 @@
-.\"	$NetBSD: mount_9p.8,v 1.15 2020/06/14 00:30:20 uwe Exp $
+.\"	$NetBSD: mount_9p.8,v 1.16 2022/02/10 13:05:07 uwe Exp $
 .\"
 .\" Copyright (c) 2007 Antti Kantee.  All rights reserved.
 .\"
@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd May 30, 2020
+.Dd Feb 10, 2022
 .Dt MOUNT_9P 8
 .Os
 .Sh NAME
@@ -31,14 +31,14 @@
 .Nd mount a file server using the 9P resource sharing protocol
 .Sh SYNOPSIS
 .Nm
-.Op Fl 46su
+.Op Fl 46Csu
 .Op Fl o Ar options
 .Op Fl p Ar port
 .Oo Ar user Ns Li \&@ Oc Ns Ar host Ns Op Li \&: Ns Ar path
 .Ar mount_point
 .Nm
 .Fl c
-.Op Fl su
+.Op Fl Csu
 .Op Fl o Ar options
 .Ar device
 .Ar mount_point
@@ -84,6 +84,10 @@ to use IPv4 addresses only.
 Forces
 .Nm
 to use IPv6 addresses only.
+.It Fl C
+Permit the kernel to cache pathname components.
+By default every time the kernel does a lookup for a component name,
+the file server will be consulted.
 .It Fl c
 Interpret
 .Ar special