Go to your theme's Functions.php
Add the following shortcode at the end and replace the $html variable with whatever you want:
PHP:
function CustomContentFooter($params, $content = null){
$html = '<hr /><p style="text-align: center;">Due to OVERWHELMING DEMAND, please allow at least 2-4 weeks for delivery.</p><hr />';
$html .= 'more cotent';
$html .= 'even more content';
return $html;
}
add_shortcode('ccfooter', 'CustomContentFooter');
Then go your theme's single-product.php and search for <?php the_content() ?>, execute short code right below it
PHP:
<div class="content" itemprop="description" itemtype="http://schema.org/Product">
<?php the_content() ?>
<?php echo do_shortcode('[ccfooter]'); ?>
</div>