[IMP] sales: updated pro-forma invoice doc

closes odoo/documentation#4496

Signed-off-by: Zachary Straub (zst) <zst@odoo.com>

content/applications/sales/sales/invoicing/proforma.rst

@@ -1,34 +1,54 @@
-========================
+==================
-Send a pro-forma invoice
+Pro-forma invoices
-========================
+==================
 
-A pro-forma invoice is an abridged or estimated invoice in advance of a
+A *pro-forma invoice* is an abridged or estimated invoice sent in advance of a delivery of goods. It
-delivery of goods. It notes the kind and quantity of goods, their value,
+notes the kind and quantity of goods, their value, and other important information, such as weight
-and other important information such as weight and transportation
+and transportation charges.
-charges. Pro-forma invoices are commonly used as preliminary invoices
+
-with a quotation, or for customs purposes in importation. They differ
+Pro-forma invoices are commonly used as preliminary invoices with a quotation. They are also used
-from a normal invoice in not being a demand or request for payment.
+for customs purposes during importation. They differ from a normal invoice in that they are not a
+demand (or request) for payment.
 
 Activate the feature
 ====================
 
-Go to :menuselection:`SALES --> Configuration --> Settings` and activate
+In order to utilize pro-forma invoices, the *Pro-Forma Invoice* feature **must** be activated. To do
-the *Pro-Forma Invoice* feature.
+that, navigate to :menuselection:`Sales app --> Configuration --> Settings`, and in the
+:guilabel:`Quotations & Orders` section, click the checkbox next to :guilabel:`Pro-Forma Invoice`.
+Then, click :guilabel:`Save` to save all changes.
 
-.. image:: proforma/proforma01.png
+.. image:: proforma/pro-forma-setting.png
    :align: center
+   :alt: The Pro-Forma Invoice feature setting in the Odoo Sales application.
 
 Send a pro-forma invoice
 ========================
 
-From any quotation or sales order, you know have an option to send a
+With the :guilabel:`Pro-Forma Invoice` feature activated, the option to send a pro-forma invoice is
-pro-forma invoice.
+now available on any quotation or sales order, via the :guilabel:`Send Pro-Forma Invoice` button.
 
-.. image:: proforma/proforma02.png
+.. image:: proforma/send-pro-forma-invoice-button.png
    :align: center
+   :alt: The Send Pro-Forma Invoice button on a typical sales order in Odoo Sales.
 
-When you click on send, Odoo will send an email with the pro-forma
+When the :guilabel:`Send Pro-Forma Invoice` button is clicked, an email pop-up appears. The
-invoice in attachment.
+:guilabel:`Recipients` field is auto-populated with the customer from the sales order or quotation.
+Then, if needed, modify the :guilabel:`Subject` field and the body of the email. The pro-forma
+invoice is automatically added as an attachment to the email.
 
-.. image:: proforma/proforma03.png
+When ready, click :guilabel:`Send`, and Odoo instantly sends the email, with the attached pro-forma
+invoice, to the customer.
+
+.. image:: proforma/pro-forma-email-message-popup.png
    :align: center
+   :alt: The email pop-up window that appears with pro-forma invoice attached in Odoo Sales.
+
+.. tip::
+   To preview what the pro-forma invoice looks like, click on the PDF at the bottom of the email
+   pop-up window *before* clicking :guilabel:`Send`. When clicked, the pro-forma invoice is
+   downloaded instantly. Open that PDF to view (and review) the pro-forma invoice.
+
+   .. image:: proforma/pro-forma-pdf.png
+      :align: center
+      :alt: Sample pro-forma invoice PDF from Odoo Sales.