[ADD] accounting: doc about snailmail (#587)

accounting/receivables/customer_invoices.rst

@@ -12,3 +12,4 @@ Customer Invoices
    customer_invoices/deferred_revenues
    customer_invoices/credit_notes
    customer_invoices/epc_qr_code
+   customer_invoices/snailmail

accounting/receivables/customer_invoices/snailmail.rst

@@ -0,0 +1,45 @@
+======================================
+Send your Invoices by Post (Snailmail)
+======================================
+
+Direct mail is a great way to capture individuals’ attention at a time where inboxes are always
+full. Odoo allows you to send invoices and follow-up reports by post, worldwide, directly from
+your database.
+
+Set up Snailmail
+================
+
+| Go to :menuselection:`Accounting --> Settings --> Snailmail` and activate the feature.
+| If you would like this option to be a default feature, enable *Send by Post* under
+  *Default Sending Options*.
+
+.. image:: media/setup_snailmail.png
+   :align: center
+   :alt: Under settings enable the snailmail feauture in Odoo Accounting
+
+Send your invoices by post
+--------------------------
+
+Open your Invoice, click on the *Send & Print* button and select *Send by Post*.
+
+.. image:: media/invoice_bypost.png
+   :align: center
+   :alt: Overview of an invoice and the option send by post available in Odoo Accounting
+
+.. important::
+   Make sure to have your customer’s address set correctly, and that it includes a country,
+   before sending the letter.
+
+Pricing
+=======
+
+| *Snailmail* is an *In-App Purchase (IAP)* service which requires prepaid stamps (=credits)
+  to work. Sending one document consumes one stamp.
+| To buy stamps, go to :menuselection:`Accounting --> Configuration --> Settings --> Snailmail`
+  and click on *Buy credits*, or go to :menuselection:`Settings --> Odoo IAP` and click on
+  *View my Services*.
+
+.. tip::
+   - If you are on Odoo Online (SAAS) and have the Enterprise version, you benefit from free trial
+     credits to test the feature.
+   - Click `here <https://iap.odoo.com/privacy#header_4>`_ to know about our *Privacy Policy*.