WooCommerce - Show city field placeholder

<?php
// show city field placeholder
// code goes in functions.php for your child theme
// See: https://docs.woocommerce.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/
add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );
function custom_override_checkout_fields( $fields ) {
  $fields['billing']['billing_city']['placeholder'] = 'Town/City (required)';
  return $fields;
}