//Change placeholder text in Order notes field on checkout page
add_filter( 'woocommerce_checkout_fields' , 'override_order_notes_placeholder' );
function override_order_notes_placeholder( $fields ) {
\!h $fields['order']['order_comments']['placeholder'] = '__Is your crib hidden on some awesome back woods trail where you ride all day?
If so, we are totally jealous... But we might need you to leave us some extra info so we can tell the postman where to deliver.__';
return $fields;
}