My WooCommerce Custom Code

<?php
/**
 * Plugin Name: My Woocommerce Custom Code
 * Plugin URI: http://www.reddit.com/r/woocommerce/comments/21g33g/custom_code_gets_overwritten_when_updating/
 * Description: My Woocommerce custom code.
 * Version: 1.0
 * Author: JAX
 * Author URI: http://www.reddit.com/r/woocommerce/comments/21g33g/custom_code_gets_overwritten_when_updating/
 * License: GPL2
 */

add_action('woocommerce_after_order_notes', 'my_custom_checkout_field');
function my_custom_checkout_field( $checkout ) {
    echo '<div id="my_custom_checkout_field"><h2>'.__('').'</h2>';
        woocommerce_form_field( 'dob', array(
    'type'          => 'text',
    'class'         => array('my-field-class form-row-wide'),
    'label'         => __('Date Of Birth'),
    'placeholder'       => __('MM/DD/YYYY'),
    'required' => true,
    ), $checkout->get_value( 'dob' ));
echo '</div>';
}
?>