Add cookbook with how to customize taxes

docs/cookbook/taxation/customize-tax-by-address.rst

@@ -9,13 +9,45 @@ as from 1st July 2021 the new taxation rules will be applied.
 
     You can learn more about new EU taxation rules `here <https://ec.europa.eu/taxation_customs/business/vat/modernising-vat-cross-border-ecommerce_en>`_.
 
-To change the way how the taxes are calculated: by billing or by shipping address, we have prepared a simple parameter
-that you need to change `sylius_core.taxation.default_strategy` in your configs:
+To change the way how the taxes are calculated; by billing or by shipping address, you need to override the service called
+`OrderTaxesProcessor.php` from `Sylius/Component/Core/OrderProcessing`.
+
+First let's copy code from original Processor to our service
+from `%kernel.project_dir%/vendor/sylius/sylius/src/Sylius/Component/Core/OrderProcessing/OrderTaxesProcessor.php` to `src/OrderProcessing/OrderTaxesProcessor.php`
+
+.. code-block:: php
+
+    <?php
+
+    //...
+
+    final class OrderTaxesProcessor implements OrderProcessorInterface
+    {
+
+    //...
+
+Then register our new service:
 
 .. code-block:: yaml
 
-    # app/config/config.yml
-    parameters:
-        sylius_core.taxation.default_strategy: false
+    # app/config/services.yaml
+        App\OrderProcessing\OrderTaxesProcessor:
+        arguments:
+            - '@sylius.provider.channel_based_default_zone_provider'
+            - '@sylius.zone_matcher'
+            - '@sylius.registry.tax_calculation_strategy'
+        tags:
+            - { name: sylius.order_processor, priority: 10 }
+
+Now we need to change the line `$billingAddress = $order->getBillingAddress()` to:
+
+.. code-block:: php
+
+    //...
+    private function getTaxZone(OrderInterface $order): ?ZoneInterface
+        {
+            $billingAddress = $order->getShippingAddress();
+            $zone = null;
+    //...
 
-And with this change, the way how taxes are calculated is based on shipping address.
+And with this change, the way how taxes are calculated will be based on shipping address.