Add content to emails sent out by woocommerce

woocommerce.emails.php

<?php 

add_action( 'woocommerce_email_before_order_table', __CLASS__ . '::before_order_email', 10, 4 );
add_action( 'woocommerce_email_after_order_table', __CLASS__ . '::after_order_email', 10, 4 );

// Add content before the order table
static function before_order_email(  $order, $sent_to_admin, $plain_text, $email ) {
  // If the emails links to the dashboard
  if ( $sent_to_admin ) {
    // email is plain text, not html
    if ( ! $plain_text ) {
      // HTML content here
    } else {
      // Plain text only
    }
  }
}

// Add content after the order table
static function after_order_email(  $order, $sent_to_admin, $plain_text, $email ) {
  // If the emails links to the dashboard
  if ( $sent_to_admin ) {
    // email is plain text, not html
    if ( ! $plain_text ) {
      // HTML content here
    } else {
      // Plain text only
    }
  }
}