[ADD] sales: Increase your sales with suggested products

Origin: https://docs.google.com/document/d/1NMIL5YHCyFl-RHbvYYcyhN23Px8PszYBamxVYPF6bN0/edit

sales/send_quotations.rst

@@ -6,3 +6,4 @@ Send Quotations
    :titlesonly:
 
    send_quotations/quote_template
+   send_quotations/optional_items

sales/send_quotations/optional_items.rst

@@ -0,0 +1,50 @@
+===========================================
+Increase your sales with suggested products
+===========================================
+
+The use of suggested products is an attempt to offer related and useful
+products to your client. For instance, a client purchasing a cellphone
+could be shown accessories like a protective case, a screen cover, and
+headset.
+
+Add suggested products to your quotation templates
+==================================================
+
+Suggested products can be set on *Quotation Templates*.
+
+.. TODO You can find documentation about it here https://docs.google.com/document/u/1/d/11UaYJ0k67dA2p-ExPAYqZkBNaRcpnItCyIdO6udgyOY/edit?usp=drive_web&ouid=104638657716670524342
+
+Once on a template, you can see a *Suggested Products* tab where you
+can add related products or services.
+
+.. image:: media/optional_items01.png
+   :align: center
+
+You can also add or modify suggested products on the quotation.
+
+Add suggested products to the quotation
+=======================================
+
+When opening the quotation from the received email, the customer can add
+the suggested products to the order.
+
+.. image:: media/optional_items02.png
+   :align: center
+
+.. image:: media/optional_items03.png
+   :align: center
+
+The product(s) will be instantly added to their quotation when clicking
+on any of the little carts.
+
+.. image:: media/optional_items04.png
+   :align: center
+
+Depending on your confirmation process, they can either digitally sign
+or pay to confirm the quotation.
+
+Each move done by the customer to the quotation will be tracked in the
+sales order, letting the salesperson see it.
+
+.. image:: media/optional_items05.png
+   :align: center