title: Add field to wordpress billing fields
body: <p>I'd like to add 2 custom fields to the user billing information in WooCommerce, one for capturing their VAT number and one for the Chamber of Commerce number. These fields need to be displayed during checkout, on the my account > billing address page and also on the WP Admin on the user page so the admin of the website/webshop can check for these values.</p>
  
  <p>I prefer not to use a plugin but to use the child theme's functions.php.</p>
  
  <p>Can anyone please help me with this problem? I looked around on the Wordpress Stack exchange but couldn't find a specific and up-to-date solution for my problem. Also I read the Woocommerce documentation but there it's not explained how to show the custom billing fields on the user admin page in the backend.</p>
  
  <p>Thank you very much in advance!</p>