Hi Greg,
Thank you for reaching out to us. This can be done with custom development, because this requires a template change, I’d advise that you setup a child theme. This allows you to make code changes that won’t be overwritten when an X update is released. After your child theme is setup, please review how we recommend making template changes in Customization Best Practices.
After setting up the child then add the following code in your child theme’s functions.php file:
add_action( 'x_before_view_global__index', 'portfolio_short_desc' );
function portfolio_short_desc() {
if(is_post_type_archive( 'x-portfolio' )){
echo "<p>Short Description</p>";
}
}
Change the text as you need. Hope this helps!