[ADD] How to cancel a shipping request to a shipper?

https://docs.google.com/document/d/1WB88l93x5_7ljpjmvvzIrzRn-6kvuTp5Si7dkssiblg/edit#

inventory/shipping/operation/cancel.rst

@@ -1,3 +1,51 @@
 ==============================================
 How to cancel a shipping request to a shipper?
 ==============================================
+
+Overview
+========
+
+Odoo can handle various delivery methods, including third party
+shippers. Odoo will be linked with the transportation company tracking
+system.
+
+It will allow you to manage the transport company, the real prices and
+the destination.
+
+You can easily cancel the request made to the carrier system.
+
+How to cancel a shipping request? 
+=================================
+
+-   If the delivery order is not **Validated**, then the request hasn’t been
+    made. You can choose to cancel the delivery or to change the
+    carrier.
+
+-   If you have clicked on **Validate**, the request has been made and you
+    should have received the tracking number and the label. You can
+    still cancel the request.
+    Simply click on the **Cancel** button next to the **Carrier Tracking Ref**:
+
+.. image:: media/cancel01.png
+   :align: center
+
+You will now see that the shipment has been cancelled.
+
+.. image:: media/cancel02.png
+   :align: center
+
+You can now change the carrier if you wish.
+
+How to send a shipping request after cancelling one? 
+====================================================
+
+After cancelling the shipping request, you can change the carrier you
+want to use. Confirm it by clicking on the **Send to shipper** button. You
+will get a new tracking number and a new label.
+
+.. image:: media/cancel03.png
+   :align: center
+
+.. seealso::
+    * :doc:`invoicing`
+    * :doc:`multipack`