[MOV] accounting: restructuration of the accounting documentation

This commit improves the structure of the accounting documentation by
- reducing the levels necessary to reach the information
- grouping some docs
- moving content to their parent category page (content in all levels)
- renaming some sections to reflect the structure of the app better

task-3330093

closes odoo/documentation#4470

Signed-off-by: Castillo Jonathan (jcs) <jcs@odoo.com>

content/applications/finance/accounting/customer_invoices/payment_terms.rst

@@ -0,0 +1,121 @@
+===================================
+Payment terms and installment plans
+===================================
+
+**Payment Terms** specify all the conditions under which a sale is paid, mostly to ensure customers
+pay their invoices correctly and on time.
+
+Payment Terms can be applied to sales orders, customer invoices, supplier bills, and contacts. These
+conditions cover:
+
+- The due date
+- Some discounts
+- Any other condition on the payment
+
+Defining Payment Terms automatically calculates the payments' due dates. This is particularly
+helpful for managing installment plans.
+
+An **installment plan** allows the customers to pay an invoice in parts, with the amounts and
+payment dates defined beforehand by the seller.
+
+**Examples of Payment Terms:**
+
+- | **Immediate Payment**
+  | The full payment is due on the day of the invoice's issuance.
+- | **15 Days** (or **Net 15**)
+  | The full payment is due 15 days after the invoice date.
+- | **21 MFI**
+  | The full payment is due by the 21st of the month following the invoice date.
+- | **2% 10, Net 30 EOM**
+  | 2% :doc:`cash discount <cash_discounts>` if the payment is received within ten days. Otherwise,
+    the full payment is due at the end of the month following the invoice date.
+
+.. note::
+   Payment terms are not to be confused with down payment invoices. If, for a specific order, you
+   issue several invoices to your customer, that is neither a payment term nor an installment plan,
+   but an invoicing policy.
+
+.. note::
+   This document is about the *Payment Terms* feature, not *Terms & Conditions*.
+
+.. seealso::
+   - :doc:`cash_discounts`
+   - `Odoo Tutorials: Payment Terms <https://www.odoo.com/slides/slide/payment-terms-1679>`_
+
+Configuration
+=============
+
+Go to :menuselection:`Accounting --> Configuration --> Payment Terms` and click on *Create*.
+
+The **Description on the Invoice** is the text displayed on the document (sale order, invoice,
+etc.).
+
+In the **Terms** section, you can add a set of rules, called *terms*, to define what needs to be
+paid and by which due date.
+
+To add a term, click on *Add a line*, and define its *Type*, *Value*, and *Due Date Computation*.
+
+.. important::
+   - Terms are computed in the order they are set up.
+   - The **balance** should always be used for the last line.
+
+In the following example, 30% is due on the day of issuance, and the balance is due at the end of
+the following month.
+
+.. image:: payment_terms/configuration.png
+   :align: center
+   :alt: Example of Payment Terms. The last line is the balance due on the 31st of the following
+         month.
+
+Using Payment Terms
+===================
+
+Payment Terms can be defined in the **Due Date** field, with the **Terms** drop-down list, on:
+
+- | **Quotations**
+  | To set specific payment terms automatically on all invoices generated from a quotation.
+- | **Customer Invoices**
+  | To set specific payment terms on an invoice.
+- | **Vendor Bills**
+  | To set specific payment terms on a bill. This is mostly useful when you need to manage vendor
+    terms with several installments. Otherwise, setting the *Due Date* is enough.
+
+.. tip::
+   You can also define a **Due Date** manually. If Payment Terms are already defined, empty the
+   field so you can select a date.
+
+Payment Terms can be defined with the **Payment Terms** field on:
+
+- | **Contacts**
+  | To set specific payment terms automatically on new sales orders, invoices, and bills of a
+    contact. This can be modified in the contact’s *Form View*, under the *Sales & Purchase* tab.
+
+Journal Entries
+===============
+
+Invoices with specific Payment Terms generate different *Journal Entries*, with one *Journal Item*
+for every computed *Due Date*.
+
+This makes for easier *Follow-ups* and *Reconciliation* since Odoo takes each due date into account,
+rather than just the balance due date. It also helps to get an accurate *Aged Receivable report*.
+
+.. image:: payment_terms/journal-entry.png
+   :align: center
+   :alt: The amount debited on the Account Receivable is split into two Journal Items with distinct
+         Due Dates
+
+In this example, an invoice of $1000 has been issued with the following payment terms: *30% is due
+on the day of issuance, and the balance is due at the end of the following month.*
+
++----------------------+-------------+---------+---------+
+| Account              | Due date    | Debit   | Credit  |
++======================+=============+=========+=========+
+| Account Receivable   | February 21 | 300     |         |
++----------------------+-------------+---------+---------+
+| Account Receivable   | March 31    | 700     |         |
++----------------------+-------------+---------+---------+
+| Product Sales        |             |         | 1000    |
++----------------------+-------------+---------+---------+
+
+The $1000 debited on the Account Receivable is split into two distinct *Journal Items*. Both of
+them have their own **Due Date**.