[ADD] sales : Setup your default terms and conditions

Origin : https://docs.google.com/document/d/1kEGDLj6rd0crgkem8NZmjSNx4V-SGKBpdE-LYDYiQwM/edit

sales/send_quotations/terms_and_conditions.rst

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+================================
+Add terms & conditions on orders
+=================================
+
+Specifying Terms and Conditions is essential to ensure a good
+relationship between customers and sellers. Every seller has to declare
+all the formal information which include products and company policy;
+allowing the customer to read all those terms everything before
+committing to anything.
+
+Odoo lets you easily include your default terms and conditions on every
+quotation, sales order and invoice.
+
+Set up your default terms and conditions
+=========================================
+
+Go to :menuselection:`SALES --> Configuration --> Settings` and activate
+*Default Terms & Conditions*.
+
+.. image:: media/terms_and_conditions01.png 
+  :align: center 
+ 
+In that box you can add your default terms & conditions. They will then
+appear on every quotation, SO and invoice.
+
+.. image:: media/terms_and_conditions02.png 
+  :align: center 
+
+Set up more detailed terms & conditions
+========================================
+
+A good idea is to share more detailed or structured conditions is to
+publish on the web and to refer to that link in the terms & conditions
+of Odoo.
+
+You can also attach an external document with more detailed and
+structured conditions to the email you send to the customer. You can
+even set a default attachment for all quotation emails sent.
+
+.. image:: media/terms_and_conditions03.png
+  :align: center