[ADD] inventory: How to limit a delivery method to a certain number of countries?

https://docs.google.com/document/d/1eohk_KxZhNI9dbQcbIKUOohqsuIi44OHLTRp02-bSms/edit

inventory/management/delivery.rst

@@ -12,4 +12,5 @@ Delivery Orders
    delivery/three_steps
    delivery/scheduled_dates
    delivery/dropshipping
-   delivery/label_type
+   delivery/label_type
+   delivery/delivery_countries

inventory/management/delivery/delivery_countries.rst

@@ -0,0 +1,41 @@
+===================================================================
+How can I limit a delivery method to a certain number of countries?
+===================================================================
+
+Overview
+========
+
+With Odoo, you can have different types of delivery methods, and you can
+limit them to a certain number of countries.
+
+Configuration
+=============
+
+Go to the **Inventory** module, click on **Configuration** and then on
+**Delivery Methods**.
+
+.. image:: media/delivery_countries01.png
+    :align: center
+
+Select the delivery method that you want to change, or create a new one.
+
+.. image:: media/delivery_countries02.png
+    :align: center
+
+In the **Destination** tab, choose the countries to which you want to
+apply this delivery method.
+
+Now, that this is done, Let's see the result.
+
+If you go to the website, and you try to buy something, once you've
+entered your details and you proceed to the payment, the website will
+propose you only the delivery methods that apply to your shipping
+address.
+
+.. image:: media/delivery_countries03.png
+    :align: center
+
+.. note::
+    This process doesn't work in backend. We assume that when you
+    create a Sale Order, you know which delivery method you can use since
+    you created them.