Add Lightning address to WordPress head

lightning-address.php

<?php

/**
 * Plugin Name:       Lightning Address
 * Plugin URI:        https://gist.github.com/Bobz-zg/5e8fe19442d88ddb32bae428dfc199f3/edit
 * Author:            Vlado Bosnjak
 * Author URI:        https://github.com/code-soup
 * Description:       Handle the basics with this plugin.
 * Version:           0.0.1
 * Requires at least: 5.2
 * Requires PHP:      7.0
 * License:           GPL v2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain:       lightning-address
 */

add_action('wp_head', function () {
    
    printf(
        '<meta name="lightning" content="lnurlp:%s"/>',
        'you@lightning.address'
    );
});