Show another way to learn about convbdf

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26172 a1c6a512-1295-4272-9138-f99709370657
diff --git a/manual/advanced_topics/main.tex b/manual/advanced_topics/main.tex
index f024e1f..1c47b67 100644
--- a/manual/advanced_topics/main.tex
+++ b/manual/advanced_topics/main.tex
@@ -22,7 +22,8 @@
     be usable with Rockbox. To convert from \fname{.bdf} to \fname{.fnt}, use
     the \fname{convbdf} tool. This tool can be found in the \fname{tools}
     directory of the Rockbox source code. See \wikilink{CreateFonts\#ConvBdf}
-    for more details.}
+    for more details. Or just run \fname{convbdf} without any parameters to
+    see the possible options.}
 }
 
 \subsection{\label{ref:Loadinglanguages}Loading Languages}