Adding star ratings to testimonials slider

So I've built a testimonials post type into my WordPress theme added it to a slider on the homepage but I'm getting confused when it comes to adding the rating given by the customers can anyone point me in the right direction im not interested in using a plugin

function custom_testimonials() {

    $labels = array(
        'name' = __( 'testimonials' ),
        'singular_name' = __( 'Testimonials' ),
        'all_items'           = __( 'All Testimonials' ),
        'view_item'           = __( 'View Testimonial' ),
        'add_new_item'        = __( 'Add New Testimonial' ),
        'add_new'             = __( 'Add New Testimonial' ),
        'edit_item'           = __( 'Edit Testimonial' ),
        'update_item'         = __( 'Update Testimonial' ),
        'search_items'        = __( 'Search Testimonials' ),
        'search_items' = __('Testimonials')
    );

    $args = array(
        'labels' = $labels,
        'description' = 'Add New Testimonial contents',
        'menu_position' = 28,
        'public' = true,
        'has_archive' = true,
        'map_meta_cap' = true,
        'capability_type' = 'post',
        'hierarchical' = true,
        'rewrite' = array('slug' = false),
        'menu_icon'='dashicons-smiley',
        'supports' = array(
            'title',
            'editor'
        ),
    );
    register_post_type( 'testimonials', $args);

}