Update add menus guide a bit.

guides/Add-Menus.md

@@ -12,7 +12,7 @@ Add my custom code define under s32 l_counter = 0 in options_menu.c, example:
 
 
 ### To add a menu into options_menu.c:
-1. Define a string using the charmap.txt into text_options_strings.h, for example to make the word "Test" add this into that file: 
+1. Define a string using the charmap.txt into text_options_strings.h, for example to make the word "Test" add this into that file (0xFF is needed at the end):
 ```
 #define TEXT_OPT_TEST      0x1D,0x0E,0x1C,0x1D,0xFF
 ```