Mention that -n does not work with openbox.

man/xdgmenumaker.t2t

@@ -68,7 +68,7 @@ you use; some window managers don't support large icons in the menu.
 : **-n, --no-submenu**
 do not create a submenu. Instead, place the application categories menus
 in the window manager's main menu. This option does not have any effect
-for //windowmaker// menus.
+for //openbox// or //windowmaker// menus.
 
 : **--max-icon-size**
 restrict the maximum size for icons to the one specified with the

src/xdgmenumaker

@@ -250,7 +250,7 @@ def usage():
     print('        --no-svg         Do not use SVG icons even for WMs that support it')
     print('    -s, --size           preferred icon size in pixels (default: 16)')
     print('    -n, --no-submenu     do not create a submenu. Does not work with')
-    print('                         windowmaker')
+    print('                         openbox and windowmaker')
     print('        --max-icon-size  restrict the icon sizes to the specified size')
     print('        --pekwm-dynamic  generate dynamic menus for pekwm')
     print('        --twm-titles     show menu titles in twm menus')