title: Checkbox field that add / remove a custom fee in WooCommerce
body: <p>Need to add custom fee to cart based on form checkbox element. Current action based on product category in cart works great and adds custom delivery fee but customer has option to pickup order which is free. Can checkbox checked for delivery trigger WooCommerce add custom fee action?</p>
  
  <p>Using example from "perform an action on checkbox checked or unchecked event on html form" can .change(function) function delivery(id){
    if(this.checked) {
  add_action for custom cart fee? </p>
  
  <pre><code> add_action( 'woocommerce_cart_calculate_fees', 'add_a_custom_fee', 10, 1 );
  function add_a_custom_fee( $cart ) {
          $amount = 25;
          $cart-&gt;add_fee( __('Custom fee'), $amount );
  }
  </code></pre>
  
  <p>Expected custom cart fee to appear in cart when checkbox checked.</p>