Manually adding code to the theme will not help. The next time the theme or wordpress itself is updated, all your changes will disappear. Because with wordpress, Twenty ten and twenty eleven themes will be automatically updated (this is where child themes come into picture). The way to do it is, go to Appearance > Menu > Custom(create your link here) and add it to the menu on the right side. Now on the right side, you can drag and drop them to arrange in the order you like. Click save and you have it.