Please update docs

Please make a small update to the docs for MB Term Meta.

I'm adding custom fields to taxonomies that get added programatically and I noticed that my metaboxes were appearing all over the place, some multiple times. it took a while to figure out why, because only part was showing up multiple times. (this was because the fieldnames are all the same, so those get added only once, but the metabox title was showing up 6 or 7 times)

It turned out that I had copied the demo code without noticing that the id of the meta-box was missing.

Please accept my suggestion to add it so that others don't make the same mistake;

add_filter( 'rwmb_meta_boxes', 'prefix_register_taxonomy_meta_boxes' );
function prefix_register_taxonomy_meta_boxes( $meta_boxes ){
    $meta_boxes[] = array(
        'title'      => 'Standard Fields',
        'taxonomies' => 'category', // List of taxonomies. Array or string
        'id' => "unique_id_goes_here",  // <-- Please add this
        'fields' => array(
            array(
                'name' => 'Featured?',
                'id'   => 'featured',
                'type' => 'checkbox',
            ),
            array(
                'name' => 'Featured Content',
                'id'   => 'featured_content',
                'type' => 'wysiwyg',
            ),
            array(
                'name' => 'Featured Image',
                'id'   => 'image_advanced',
                'type' => 'image_advanced',
            ),
            array(
                'name' => 'Color',
                'id'   => 'color',
                'type' => 'color',
            ),
        ),
    );
    return $meta_boxes;
}