Guidebook.tex bit

Backslash doesn't need to be escaped by backslash inside a verbatim
block (presumably the first character is an exception).  The doubled
backslashes in SOUNDDIR example were producing doubled backslashes in
the output.

There didn't seem to be any other instances of this.

doc/Guidebook.tex

@@ -5918,7 +5918,7 @@ The pattern should be a POSIX extended regular expression.
 For example:
 
 \begin{verbatim}
-    SOUNDDIR=C:\\nethack\\sounds
+    SOUNDDIR=C:\nethack\sounds
     SOUND=MESG "This door is locked" "lock.wav" 100
     SOUND=MESG hide "^You miss the " "swing.wav" 75
 \end{verbatim}