Automatically Add a Disclaimer to WordPress Posts

/**
 * Add a custom disclaimer to WordPress posts
 */
function custom_post_disclaimer( $content ) {

    if ( ! is_single() || ! is_main_query() || ! in_the_loop() ) {
        return $content;
    }

    $disclaimer  = '<div class="post-disclaimer">';
    $disclaimer .= '<strong>Disclaimer:</strong> ';
    $disclaimer .= 'The information provided in this article is for general informational purposes only.';
    $disclaimer .= '</div>';

    return $content . $disclaimer;
}

add_filter( 'the_content', 'custom_post_disclaimer' );