Add a small introduction before editor content meta box

editor-intro.php

/**
 * Add a little intro above the post editor screen for Job_post CPT. 
 */
add_action( 'edit_form_after_title', 'prefix_add_editor_intro' );
function prefix_add_editor_intro() {
	global $post, $post_type;
	if( is_admin() && 'job_posting' == $post_type ) { 
		echo 'Enter full job description in box below, including, but not limited to: education requirements, experience needed, recommended skills, job responsibilities, benefits, application requirements, salary, etc.';
	}
}