[ADD] sale: How to display optional products on a quotation?

https://docs.google.com/document/d/1KrTite1f47uAxv9QJPhucTnAlzgz38YGEOlWQdO3ar8/edit
https://docs.google.com/document/d/1XXksQhCVostQB43GvHiy1xAVoa0VL_MS8y87Silz0So/edit

sales/quotation/setup.rst

@@ -7,3 +7,4 @@ Setup
 
    setup/first_quote
    setup/different_addresses
+   setup/optional

sales/quotation/setup/optional.rst

@@ -1,3 +1,75 @@
 ================================================
 How to display optional products on a quotation?
-================================================
+================================================
+
+Overview
+========
+
+The use of suggested products is a marketing strategy that attempts 
+to increase the amount a customer spends once they begin the buying 
+process. For instance, a customer purchasing a cell phone could be 
+shown accessories like a protective case, a screen cover, and headset. 
+In Odoo, a customer can be presented with additional products that are 
+relevant to their chosen purchase in one of several locations.
+
+This document covers the configuration and use of suggested products in Odoo.
+
+
+Configuration
+=============
+
+Suggested products can be added to quotations directly, or to the ecommerce 
+platform via each product form. In order to use suggested products, you will
+need to have the **Ecommerce** applications installed:
+
+Product
+-------
+
+On the product form view, under the **Sales** tab, you can set optional products 
+on that will be proposed on an order each time that this product is added in the 
+cart or on the sale order. On the picture below, we set 2 optional products on a
+computer case. 
+
+.. image:: media/optional01.png
+    :align: center
+
+Quotation template
+------------------
+
+We can configure also configure optional products on quotation template like on the 
+picture below.
+
+.. image:: media/optional02.png
+    :align: center
+
+For online quotation design you can follow following topic: :doc:`../online/creation`
+
+Orders with optional product
+============================
+
+Online order
+------------
+
+Now, if a customer is adding in his cart the Computer Case product on which we set 
+2 suggested products, 
+
+.. image:: media/optional03.png
+    :align: center
+
+on the same page are displayed these 2 products that they can add to their cart too.
+
+.. image:: media/optional04.png
+    :align: center
+
+The customer can after that complete the sale process from the checkout to the payment. 
+For more information on sales you can follow another topic: :doc:`../../overview/process/from_quote_to_so`
+
+Quotation backend
+-----------------
+
+We are creating a quotation in the sales application by using a template. The system will 
+propose on the sale order form under the **Suggested Products** tab the products that were
+defined on the template. 
+
+.. image:: media/optional06.png
+    :align: center