Straight from the WordPress documentation for registering_post_type in the code you are registering your custom post type you should be able to add: ‘show_in_nav_menus’ => true, and that should allow your post type to show in navigation menus. Here’s the documentation for the register_post_type function
Adding a link in your menu straight to the page also works, but in my opinion it is very messy. It would seem not many people are aware of the show_in_nav_menus argument of register_post_type because by default the value is set to false.
Hope this helps you.