Make include directives work in .mnu files

doc/formats/mnu.md

@@ -134,6 +134,16 @@ $GenLoad.mni
 It looks like we just interpolate the named file into the text when we come
 across one of these lines.
 
+The `MENUID` in `GenDialog` and `GenLoad` is a 2-element list, like `1000,1`
+or `2000,2`. The second number corresponds to the offset in the list of object
+files.
+
+## `MENUTYPE`
+
+Here's the full list of 
+
+## `SUBMENUTYPE`
+
 ## (Sub)menu types
 
 The types seem to refer to different types of UI widget. Here's a list of unique