title: Woocommerce minimum order by category/quantity
body: <p>I'm wondering if it would be possible to create an if statement where if a customer hasn't added enough (quantity - not price) of a specific product category to their order, a message shows up saying they need to add more to avoid a surcharge. I'm thinking something along the lines of the minimum order amount snippet <a href="http://docs.woothemes.com/document/minimum-order-amount/" rel="nofollow">documented here</a>:</p>
  
  <pre><code>add_action( 'woocommerce_checkout_process', 'wc_minimum_order_amount' );
      function wc_minimum_order_amount() {
          global $woocommerce;
          $minimum = 50;
      if ( $woocommerce-&gt;cart-&gt;total() &lt; $minimum ) {
          $woocommerce-&gt;add_error( sprintf( 'You must have an order with a minimum of %s to place your order.' , $minimum ) );
      }
  }
  </code></pre>
  
  <p>Any help would be greatly appreciated.</p>