Top Level Logout Admin Menus Button

I am trying to create a ‘log out’ button in the administrative menu, in the dashboard on the left.

I have tried working with this and editing it accordignly, right out of the codex:

<?php add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position ); ?>

But I can’t even get that to display on the admin menu. Not sure what I am doing wrong. I just want to create a link in the admin menu that log the user out, so I can remove that ‘Howdy’ menu up in the admin bar.

Any help would be greatly appreciated!