[ADD] subscriptions: add base documentation for Subscriptions (#617)

* [ADD] subscriptions: add base documentation for Subscriptions

* [ADD] subscriptions/sales_flow/create_a_quotation: new content

* [ADD] subscriptions/sales_flow/renewals: new content

* [ADD] subscriptions/sales_flow/upselling: new content

* [ADD] subscriptions/sales_flow/closing: new content

* [ADD] subscriptions/reporting/subscription_reports: new content

subscriptions/configuration/subscription_templates.rst

@@ -0,0 +1,91 @@
+==========================
+Use subscription templates
+==========================
+
+The subscription business model is becoming more popular. Are you wondering why?
+
+- For **customers**, value lies in **convenience**:
+
+  - Subscriptions simplify the business process. Indeed, subscribers never have to remember to renew
+    their orders every month, which gives them the assurance that they will have everything they
+    need before they actually need it.
+  - Subscriptions help customers stay on budget.
+
+- For **businesses**, value lies in the **ability to predict recurring revenue**:
+
+  - Subscriptions reduce customer churn rate and significantly increase customer retention.
+  - Subscriptions provide much higher payment security for your business. They stabilize and
+    maintain recurring revenue streams by guaranteeing monthly revenues and adding value to your
+    business.
+
+.. raw:: html
+
+   <div align="center" style="color:#AD5E99; font-size: 2rem ;margin: 20px 0"> <b>Simplicity.
+   Higher customer retention. Opportunities for marketing. Business consistency. Better cash flow
+   management.</b> </div>
+
+**Odoo Subscriptions** help you save time and money. Subscription templates can help you generate
+recurring invoices and manage renewals at a fast pace. With Odoo you have the possibility to create,
+edit, and manage your own subscription templates.
+
+Configuration
+=============
+
+Go to :menuselection:`Subscriptions --> Configuration --> Subscription templates`. By default, Odoo
+suggests you two types of subscription (MON - Monthly subscription *vs* YEA - Yearly subscription).
+You can also create your own ones.
+
+.. image:: media/subscription_templates_1.png
+  :align: center
+  :alt: Default subscription templates on Odoo Subscriptions
+
+.. important::
+   The **Odoo Subscriptions** application automatically installs **Odoo Sales** and **Odoo Invoicing**
+   as they work integrated.
+
+Create your first template
+==========================
+
+You can create a new template or edit an existing one. The first thing you need to do is give your
+template a name. After that, choose an *Invoicing period* and specify whether you would like to
+invoice your customers per *Days*, *Weeks*, *Months* or *Years*. On *Duration*, determine if
+the subscription must go on *Forever* (until it’s manually closed), or for a *Fixed amount* of time.
+Among the payment options, an additional field called *Invoice email* appears when you choose
+*Send*, *Send & try to charge* or *Send after successful payment*. This field allows you to add an
+invoice email template to your subscription templates.
+
+.. image:: media/subscription_templates_2.png
+  :align: center
+  :alt: Create your own subscription templates on Odoo Subscriptions
+
+For each template, you can also choose if you want your customers to be able to close their
+subscriptions or not. If enabled, you can set an *Automatic closing* limit and specify the
+*Group of subscription* and *Journal* options.
+
+.. note::
+   On each template, you can add your **Terms and Conditions**. Specifying terms and conditions is
+   essential to set out important contractual points between the customers and the sellers (payment,
+   refund policy, cancellation, complaints, etc.).
+
+   .. image:: media/subscription_templates_3.png
+     :align: center
+     :alt: Terms & conditions on Odoo Subscriptions
+
+   Finally, if you want to know the basic running health status of your subscriptions, you also have
+   access to a specific tab called **Health Check**. There, you can edit and create your own
+   filters to define what is a subscription in good health *vs* bad health. The system automatically
+   summarizes all the records corresponding to these filters and you are able to manage them in one
+   click.
+
+   .. image:: media/subscription_templates_4.png
+     :align: center
+     :alt: Health check on Odoo Subscriptions
+
+.. important::
+   After creating your own subscription templates, be sure to check out our documentation on how to
+   create, edit and manage your own
+   :doc:`Subscription products <../../subscriptions/configuration/subscription_products>`,
+   to complete the sales flow.
+
+.. seealso::
+  - :doc:`../../subscriptions/configuration/subscription_products`