wordpress怎么自动在正文内容后添加内容

function insertFootNote($content) { 
    if(!is_feed() && !is_home()) { 
        $content.= <div class='subscribe'>; 
        $content.= <h4>Enjoyed this article?</h4>; 
        $content.= <p>Subscribe to our <a href='http://feed.gree020.cn/'>RSS feed</a> and never miss a recipe!</p>; 
        $content.= </div>; 
    } 
    return $content; 
} 
add_filter ('the_content', 'insertFootNote');