some updates to make nethack.6 less dated.

doc/nethack.6

@@ -64,8 +64,7 @@ nethack \- Exploring The Mazes of Menace
 is a display oriented Dungeons & Dragons(tm) - like game.
 The standard tty display and command structure resemble rogue.
 .PP
-Other, more graphical display options exist if you are using either a PC,
-or an X11 interface.
+Other, more graphical display options exist for most platforms.
 .PP
 To get started you really only need to know two commands.  The command
 .B ?
@@ -77,8 +76,11 @@ will identify the things you see on the screen.
 To win the game (as opposed to merely playing to beat other people's high
 scores) you must locate the Amulet of Yendor which is somewhere below
 the 20th level of the dungeon and get it out.
-Nobody has achieved this yet; anybody who does will probably go down
-in history as a hero among heroes.
+Few people achieve this; most never do.  Those who have go down
+in history as heros among heroes - and then they find ways of making the
+game even harder.  See the
+.I Guidebook
+section on Conduct if this game has gotten too easy for you.
 .PP
 When the game ends, whether by your dying, quitting, or escaping
 from the caves,