Source code for https://victorfont.com/crawl-delay-10-in-robots-txt/

robots_mod.php

<?php

//* Append directives to the virtual robots.txt
//* Siteground adds crawl-delay: 10 to robots.txt. Don't use physical robots.txt on SiteGround
add_filter( 'robots_txt', 'robots_mod', 10, 2 );
function robots_mod( $output, $public ) {
    $output .= "Sitemap: https://victorfont.com/sitemap_index.xml";
    return $output;
}