Refer to relevant config options in the Guidebook

Give the reader a hint what to look for if they want to configure
the message line.

doc/Guidebook.mn

@@ -359,6 +359,11 @@ things that are impossible to represent visually.  If you see a
 another message to display on the screen, but it wants to make certain
 that you've read the one that is there first.  To read the next message,
 just press the space bar.
+.pg
+To change how and what messages are shown on the message line,
+see ``Configuring Message Types`` and the
+.op verbose
+option.
 .hn 2
 The map (rest of the screen)
 .pg

doc/Guidebook.tex

@@ -428,6 +428,11 @@ another message to display on the screen, but it wants to make certain
 that you've read the one that is there first.  To read the next message,
 just press the space bar.
 
+%.pg
+To change how and what messages are shown on the message line,
+see ``{\it Configuring Message Types\/}`` and the {\it verbose\/}
+option.
+
 %.hn 2
 \subsection*{The map (rest of the screen)}