Show custom text after author name

<?php
/*
Plugin Name: AW Author Box
Plugin URI: http://www.damiencarbery.com
Description: For Riyad Arefin in Advanced WordPress Facebook group.
Author: Damien Carbery
Version: 0.1

$Id:  $
*/

add_filter('the_content', 'aw_author_box', 30);
function aw_author_box($content) {
    $user_id = get_the_author_meta('ID');

    // Start with the lowest capability.
    if (user_can($user_id, 'read')) $user_string = 'Subscriber';
    if (user_can($user_id, 'edit_posts')) $user_string = 'Contributor';
    if (user_can($user_id, 'edit_published_posts')) $user_string = 'Author';
    if (user_can($user_id, 'moderate_comments')) $user_string = 'Editor';
    if (user_can($user_id, 'activate_plugins')) $user_string = 'Administrator';

    $author_box = sprintf('Author: <a href="%s">%s</a> (%s)', get_author_posts_url($user_id), get_the_author_meta('display_name'), $user_string );
    return $content . $author_box;
}