[ADD] pos: how to add/modify customer notes from POS UI

Task ID: 2622090

closes odoo/documentation#3955

Signed-off-by: Platteau Xavier (xpl) <xpl@odoo.com>

content/applications/sales/point_of_sale/overview.rst

@@ -8,6 +8,7 @@ Overview
    :titlesonly:
 
    overview/getting_started
+   overview/customer_note
    overview/register
    overview/https
    overview/epos_ssc

content/applications/sales/point_of_sale/overview/customer_note.rst

@@ -0,0 +1,38 @@
+=============
+Customer note
+=============
+
+The **Customer note** feature allows you to provide customers with further information on a specific
+product. For instance, to provide cleaning and maintenance tips. They can also be used to track a
+customer’s particular request, such as not wanting the product to be assembled for them.
+
+Add a customer note
+===================
+
+You can add notes directly from an open :ref:`POS session <pos/start-session>`. To do so, click
+:guilabel:`Customer Note` on the pad. Doing so opens a pop-up window in which you can add content
+for the note.
+
+.. note::
+   Product notes from an :doc:`imported SO <../shop/sales_order>` are displayed identically in the
+   cart.
+
+.. image:: customer_notes/customer-notes-ui.png
+   :align: center
+   :alt: customer note button and notes (SO and POS session) on products in the cart
+
+Modify a customer note
+======================
+
+Select the product from the cart to modify an existing note and click :guilabel:`Customer Note`.
+Doing so reopens the previous pop-up window. Alter the text and click :guilabel:`Add`.
+
+Receipts and invoices
+=====================
+
+Customer notes appear on customers' receipts and invoices similarly to how they appear in the cart,
+meaning under the related product.
+
+.. image:: customer_notes/notes-receipt.png
+   :align: center
+   :alt: customer receipt with notes from an SO and from the customer note feature