title: How to add / remove columns in Woocommerce admin product list
body: <p>I want to customize the columns in Woocommerce admin area when viewing the product list.</p>
  
  <p>Specifically, I want to remove some columns, and add several custom field columns.</p>
  
  <p>I tried many solutions listed online, and I can remove columns and add new ones like this:</p>
  
  <pre><code>add_filter( 'manage_edit-product_columns', 'show_product_order',15 );
  function show_product_order($columns){
  
     //remove column
     unset( $columns['tags'] );
  
     //add column
     $columns['offercode'] = __( 'Offer Code'); 
  
     return $columns;
  }
  </code></pre>
  
  <p>But how do I populate the new column with the actual product data (in this case, a custom field called 'offercode')?</p>