It all depends on your needs, if you need to add and update often the menu entries you probably nedd and add-on, if you only need to add an entry to menu and forget about it just edit the file sources/subs/Menu.subs.php.
here an example, I added the entry "Guide" which points to mydomain/index.php?page=guide_e_tutorial, just after the Likes Stats:
find:
'like_stats' => array(
'title' => $txt['like_post_stats'],
'href' => $scripturl . '?action=likes;sa=likestats',
'show' => !empty($modSettings['likes_enabled']) && allowedTo('like_posts_stats'),
),
and add after:
'custom_link_guide' => array(
'title' => 'Guide e tutorial',
'href' => $scripturl . '?page=guide_e_tutorial',
'show' => true,
),
sources/subs/Menu.subs.php only for Elkarte 1.1.x
sources/Subs.php for Elkarte 1.0.x