Add multifont to the manual.  Closes FS#11294.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26987 a1c6a512-1295-4272-9138-f99709370657
diff --git a/manual/advanced_topics/viewports/grayscale-vp-syntax.tex b/manual/advanced_topics/viewports/grayscale-vp-syntax.tex
index fdcdabb..a846070 100644
--- a/manual/advanced_topics/viewports/grayscale-vp-syntax.tex
+++ b/manual/advanced_topics/viewports/grayscale-vp-syntax.tex
@@ -6,7 +6,8 @@
       \item `fgshade' and `bgshade' are numbers in the range 0 (= black) to 3
       (= white).
       \item `font' is a number: 0 is the built-in system font, 1 is the
-      user-selected font.
+      current menu font, and 2-9 are additional are skin loaded fonts (see 
+      \reference{ref:multifont}).
       \item Only the coordinates \emph{have} to be specified. Leaving the other
       definitions blank will set them to their default values.
     \end{itemize}