[ADD] accounting: How to create customized reports with your own formulas ?

https://docs.google.com/document/d/131Xzg6AblBrlMl9km1fWdOSdg5BG4Ahjhw200jmPau8/edit#heading=h.70ldvcnlkutn

accounting/others/reporting.rst

@@ -5,4 +5,5 @@ Reporting
 .. toctree::
    :titlesonly:
 
-   reporting/main_reports
+   reporting/main_reports
+   reporting/customize

accounting/others/reporting/customize.rst

@@ -0,0 +1,98 @@
+=========================================================
+How to get a customized reports with your own formulas ?
+=========================================================
+
+Overview
+========
+
+Odoo 9 comes with a powerful and easy-to-use reporting framework.
+Creating new reports (such as a tax report or a balance sheet for a
+specific country) to suit your needs is now easier than ever.
+
+Activate the developer mode
+===========================
+
+In order to have access to the financial report creation interface, the
+**developer mode** needs to be activated. To do that, first click the
+**?** at the top right, then **About**.
+
+.. image:: media/customize01.png
+   :align: center
+
+Click on : **Activate the developer mode**.
+
+.. image:: media/customize03.png
+   :align: center
+
+Create your financial report
+============================
+
+First, you need to create your financial report. To do that, go to
+:menuselection:`Accounting --> Configuration --> Financial Reports`
+
+.. image:: media/customize02.png
+   :align: center
+
+Once the name is filled, there are two other parameters that need to be
+configured:
+
+-  **Show Credit and Debit Columns**
+
+-  **Analysis Period** :
+
+   -  Based on date ranges (eg Profit and Loss)
+
+   -  Based on a single date (eg Balance Sheet)
+
+   -  Based on date ranges with 'older' and 'total' columns and last 3
+      months (eg. Aged Partner Balances)
+
+   -  Bases on date ranges and cash basis method (eg Cash Flow
+      Statement)
+
+Add lines in your custom reports
+=================================
+
+After you've created the report, you need to fill it with lines. They
+all need a **name**, a **code** (that is used to refer to the line), a 
+**sequence number** and a **level** (Used for the line rendering).
+
+.. image:: media/customize04.png
+   :align: center
+
+In the **formulas** field you can add one or more formulas to assign a
+value to the balance column (and debit and credit column if applicable –
+separated by ;)
+
+You have several objects available in the formula :
+
+-  ``Ndays`` : The number of days in the selected period (for reports with a
+   date range).
+
+-  Another report, referenced by its code. Use ``.balance`` to get its
+   balance value (also available are ``.credit``, ``.debit`` and
+   ``.amount_residual``)
+
+A line can also be based on the sum of account move lines on a selected
+domain. In which case you need to fill the domain field with an Odoo
+domain on the account move line object. Then an extra object is
+available in the formulas field, namely ``sum``, the sum of the account
+move lines in the domain. You can also use the group by field to group
+the account move lines by one of their columns.
+
+Other useful fields :
+
+-  **Type** : Type of the result of the formula.
+
+-  **Is growth good when positive** : Used when computing the comparison
+   column. Check if growth is good (displayed in green) or not.
+
+-  **Special date changer** : If a specific line in a report should not use
+   the same dates as the rest of the report.
+
+-  **Show domain** : How the domain of a line is displayed. Can be foldable
+   (``default``, hidden at the start but can be unfolded), ``always``
+   (always displayed) or ``never`` (never shown).
+
+.. seealso::
+    * :doc:`main_reports`