Document .In, based on the documentation in groff-1.18.1.

Noted missing by perry.

share/man/man7/mdoc.7

@@ -1,4 +1,4 @@
-.\"	$NetBSD: mdoc.7,v 1.25 2003/04/11 09:56:07 jdc Exp $
+.\"	$NetBSD: mdoc.7,v 1.26 2003/04/16 16:05:56 wiz Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -33,7 +33,7 @@
 .\"
 .\"	@(#)mdoc.7	8.2 (Berkeley) 12/30/93
 .\"
-.Dd November 24, 1997
+.Dd April 16, 2003
 .Os
 .Dt MDOC 7
 .Sh NAME
@@ -319,6 +319,7 @@ Produces:
 .It Li \&Fn Ta Yes Ta Yes Ta "Function call (also .Fo and .Fc)."
 .It Li \&Ft Ta Yes Ta Yes Ta "Function type."
 .It Li \&Ic Ta Yes Ta Yes Ta "Interactive command."
+.It Li \&In Ta \&No Ta \&No Ta "Include header."
 .It Li \&Lb Ta Yes Ta Yes Ta "Library name."
 .It Li \&Li Ta Yes Ta Yes Ta "Literal text."
 .It Li \&Nd Ta \&No Ta \&No Ta "Name description."

share/man/man7/mdoc.samples.7

@@ -1,4 +1,4 @@
-.\"	$NetBSD: mdoc.samples.7,v 1.38 2003/04/04 19:25:40 wiz Exp $
+.\"	$NetBSD: mdoc.samples.7,v 1.39 2003/04/16 16:05:56 wiz Exp $
 .\"
 .\" Copyright (c) 1990, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -37,7 +37,7 @@
 .\" times and is guaranteed to give a worst case performance
 .\" for an already extremely slow package.
 .\"
-.Dd April 4, 2003
+.Dd April 16, 2003
 .Os
 .Dt MDOC.SAMPLES 7
 .Sh NAME
@@ -1147,6 +1147,23 @@ on the next line).
 The
 .Ql \&.Ft
 request is not callable by other macros.
+.Pp
+The
+.Ql .In
+.Li ( #include
+statement)
+macro is the short form for
+.Dl Li \&.Ft #include <header.h> .
+It specifies the C\~header file as being included in a C\~program.
+It also causes a line break, and is neither callable nor parsed.
+.Pp
+.Dl Usage: .In Ao header file Ac
+.Pp
+.Bl -tag -width ".Li .In\ stdio.h" -compact -offset 15n
+.It Li ".In stdio.h"
+.In stdio.h
+.El
+.
 .Ss Interactive Commands
 The
 .Ql \&.Ic