common, menu: show menu on startup if CONFIG_MENU_SHOW is defined

show a menu on startup instead running the shell.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Jason Hobbs <jason.hobbs@calxeda.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Acked-by: Jason Hobbs <jason.hobbs@calxeda.com>
diff --git a/doc/README.menu b/doc/README.menu
index 4ddf914..6ce6bba 100644
--- a/doc/README.menu
+++ b/doc/README.menu
@@ -25,6 +25,11 @@
 Menus are composed of items. Each item has a key used to identify it in
 the menu, and an opaque pointer to data controlled by the consumer.
 
+If you want to show a menu, instead starting the shell, define
+CONFIG_MENU_SHOW. You have to code the int menu_show(int bootdelay)
+function, which handle your menu. This function returns the remaining
+bootdelay.
+
 Interfaces
 ----------
 #include "menu.h"