[ADD] inventory: How to cancel a delivery order?

https://docs.google.com/document/d/1--3Nj9Y_pnTAFyJj0aoL5wy0ZxOUaBTCOpK2UQKwLoA/edit

inventory/management/delivery.rst

@@ -14,4 +14,5 @@ Delivery Orders
    delivery/dropshipping
    delivery/label_type
    delivery/packaging_type
-   delivery/delivery_countries
+   delivery/delivery_countries
+   delivery/cancel_order

inventory/management/delivery/cancel_order.rst

@@ -0,0 +1,42 @@
+=================================
+How do I cancel a delivery order?
+=================================
+
+Overview
+========
+
+Odoo gives you the possibility to cancel a delivery method whether it
+has been validated to fast, it needs to be modified or for any other
+reason.
+
+Some carriers are more flexible than others, so make sure to cancel your
+delivery order as fast as possible if it needs to be done so you don't
+have any bad surprise.
+
+Sale process
+============
+
+Go to the **Sales** module, click on **Sales** and then on **Sales
+Order**. Then click on the sale order you want to cancel.
+
+.. image:: media/cancel_order01.png
+    :align: center
+
+Click on the **Delivery** button, in the upper right corner of the sale
+order.
+
+.. image:: media/cancel_order02.png
+    :align: center
+
+Now, click on the **Additional info** tab and you will see that next to
+the **Carrier Tracking Reference**, there is a **Cancel** button. Click
+on it to cancel the delivery.
+
+.. image:: media/cancel_order03.png
+    :align: center
+
+To make sure that your delivery is cancelled, check in the history, you
+will receive the confirmation of the cancellation.
+
+.. image:: media/cancel_order04.png
+    :align: center