[ADD] point_of_sale: How to transfer a customer from table?

https://docs.google.com/document/d/10skoFkCTwSDmFfe3Ow5nUMLTCvwT1Q8AO825Vc7j5v8/edit#

point_of_sale/restaurant.rst

@@ -10,3 +10,4 @@ Advanced Restaurant Features
    restaurant/split
    restaurant/print
    restaurant/tips
+   restaurant/transfer

point_of_sale/restaurant/transfer.rst

@@ -0,0 +1,38 @@
+======================================
+How to transfer a customer from table?
+======================================
+
+This only work for Point of Sales that are configured in restaurant
+mode.
+
+From the dashboard, click on **New Session**.
+
+.. image:: media/transfer01.png
+    :align: center
+
+Choose a table, for example table ``T1`` and start registering an order.
+
+.. image:: media/transfer02.png
+    :align: center
+
+Register an order. For some reason, customers want to move to table ``T9``.
+Click on **Transfer**.
+
+.. image:: media/transfer03.png
+    :align: center
+
+Select to which table you want to transfer customers.
+
+.. image:: media/transfer04.png
+    :align: center
+
+You see that the order has been added to the table ``T9``
+
+.. image:: media/transfer05.png
+    :align: center
+
+.. seealso::
+    * :doc:`../shop/cash_control`
+    * :doc:`../shop/invoice`
+    * :doc:`../shop/refund`
+    * :doc:`../shop/seasonal_discount`