add missing copyright info

doc/nethack.6

@@ -1,5 +1,17 @@
-.TH NETHACK 6 "7 December 2015"
-.\" NetHack 3.6  nethack.6	$NHDT-Date: 1519228609 2018/02/21 15:56:49 $  $NHDT-Branch: githash $:$NHDT-Revision: 1.13 $
+.TH NETHACK 6 "2 February 2018" NETHACK
+.de ND
+.ds Nd \\$3
+..
+.de NB
+.ds Nb \\$2
+..
+.de NR
+.ds Nr \\$2
+..
+.ND $NHDT-Date: 1524689549 2018/04/25 20:52:29 $
+.NB $NHDT-Branch: NetHack-3.6.0 $
+.NR $NHDT-Revision: 1.14 $
+.ds Na Robert Patrick Rankin
 .SH NAME
 nethack \- Exploring The Mazes of Menace
 .SH SYNOPSIS
@@ -378,7 +390,9 @@ dgn_comp(6), lev_comp(6), recover(6)
 .SH BUGS
 .PP
 Probably infinite.
-
-
+.SH COPYRIGHT
+This file is Copyright (C) \*(Na and was last modified \*(Nd (version
+\*(Nb:\*(Nr).
+NetHack may be freely redistributed.  See license for details.
 .PP
 Dungeons & Dragons is a Trademark of Wizards of the Coast, Inc.