Add a contextual help tab to the screen

help.php

<?php

add_action('current_screen', 'jpb_current_screen');

/**
 * @param WP_Screen $screen The current screen object
 */
function jpb_current_screen($screen){
	if($screen->post_type === 'my_custom_post_type'){
		$screen->add_help_tab(array(
			'id' => 'unique_id',
			'title' => 'Human Readable Title',
			'content' => "<p>This is the help text</p>
<p>It's just HTML, so you can do anything you want with it</p>",
		));
	}
}