[ADD] purchase: difference between purchase order, tender and rfq

Based on https://docs.google.com/document/d/1X0kBpPsN1pkKyqKfX3JTXB7Tam2rgaYFkmHgV0TeP7Q/edit#

applications.rst

@@ -8,5 +8,6 @@ Applications
    accounting
    crm
    expenses
+   purchase
    recruitment
    warehouse

purchase.rst

@@ -0,0 +1,11 @@
+:banner: banners/purchase.png
+
+========
+Purchase
+========
+
+.. toctree::
+   :titlesonly:
+
+   purchase/overview
+   purchase/purchases

purchase/overview.rst

@@ -0,0 +1,9 @@
+========
+Overview
+========
+
+.. toctree::
+   :titlesonly:
+
+   overview/difference
+   overview/from_po_to_invoice

purchase/overview/difference.rst

@@ -0,0 +1,91 @@
+=========================================================
+Request for Quotation, Purchase Tender or Purchase Order?
+=========================================================
+
+Although they are intimately related, Requests for Quotation, Purchase
+Tenders and Purchase Orders are not the same.
+
+A **Request for Quotation** (RfQ) is used when you plan to purchase
+some products and you would like to receive a quote for those
+products. In Odoo, the Request for Quotation is used to send your list
+of desired products to your supplier. Once your supplier has answered
+your request, you can choose to go ahead with the offer and purchase
+or to turn down the offer.
+
+A **Purchase Tender** (PT), also known as Call for Bids, is used to
+drive competition between several suppliers in order to get the best
+offer for a list of products. In comparison to the RfQ, a Purchase
+Tender is sent to multiple suppliers, stating each are competing with
+one another, and that the best offer will win. The main interest is that
+it usually leads to better offers.
+
+The **Purchase Order** (PO) is the actual order that you place to the
+supplier that you chose, either through a RfQ, a Purchase Tender, or
+simply when you already know which supplier to order from.
+
+When to use?
+============
+
+A **RfQ** is interesting when you have never purchased the products with
+that supplier before and therefore don’t know their price. It is also
+useful if you want to challenge your suppliers once you have a
+well-established relationship with them. You can also use it to assess
+the cost of a project and see if it makes it feasible.
+
+A **Purchase Tender** is used for public offers that require an open
+offering from several suppliers. It is also useful when you need to make
+a one-off order for a product and you would like to get the best offer,
+no matter which supplier it is. It may be used when your supplier has
+not been up to your standards and you would like to either push them to
+deliver a better service, or find a replacement in their competitors.
+
+When not to use?
+================
+
+**RfQ**\ s become unnecessary once you have established your favorite
+supplier for each item, and will only increase the delay in the delivery
+of your items. In that case, the process will be simpler by starting
+straight from a Purchase Order.
+
+**Purchase Tenders** are a long and tedious process that will likely
+take more than several weeks in the best cases. If you need a quick
+delivery, this is not the way to go. Also, if you have a
+well-established relationship with one supplier, think twice before you
+initiate a PT with them as it might tear the relationship and finally
+lead to less interesting deals.
+
+Example
+=======
+
+My company builds wooden furniture. For the new series of table we are
+designing, we need some screws, metal frames and rubber protections.
+
+I create a Request for Quotation in Odoo with those products to my usual
+supplier, and send it by email. He answers back with an offer. However,
+I am not convinced by the offer, and I want to see if anyone can give a
+better one.
+
+I decide to push competition a bit and set up a Purchase Tender, that
+Odoo will send to a list of suppliers I specified. Out of the 8 offers I
+receive, one gets my attention and I decide to go ahead with that one.
+
+I confirm the order to the supplier by creating a Purchase Order from
+the PT, and Odoo automatically asks delivery of the items to the
+supplier.
+
+Configuration
+=============
+
+If you want to know how to create a **Purchase Order**, read the
+documentation on :doc:`from_po_to_invoice`
+
+If you want to know how to create a **RfQ**, read the documentation
+on :doc:`../purchases/rfq/create`
+
+If you want to know how to create a **Purchase Tender**, read the
+documentation on :doc:`../purchases/tender/manage_multiple_offers`
+
+.. rst-class:: text-muted
+
+| Written by Samuel Cabodi (Odoo)
+| Proofread by Geoffrey Bressan (Odoo)

purchase/overview/from_po_to_invoice.rst

@@ -0,0 +1,4 @@
+=============================================
+From purchase order to invoice and receptions
+=============================================
+

purchase/purchases.rst

@@ -0,0 +1,9 @@
+=========
+Purchases
+=========
+
+.. toctree::
+   :titlesonly:
+
+   purchases/rfq
+   purchases/tender

purchase/purchases/rfq.rst

@@ -0,0 +1,8 @@
+========================
+Request for Quotatations
+========================
+
+.. toctree::
+   :titlesonly:
+
+   rfq/create

purchase/purchases/rfq/create.rst

@@ -0,0 +1,4 @@
+======================================
+How to create a Request for Quotation?
+======================================
+

purchase/purchases/tender.rst

@@ -0,0 +1,8 @@
+================
+Purchase Tenders
+================
+
+.. toctree::
+   :titlesonly:
+
+   tender/manage_multiple_offers

purchase/purchases/tender/manage_multiple_offers.rst

@@ -0,0 +1,4 @@
+===================================================================
+How to manage multiple offers from suppliers with purchase tenders?
+===================================================================
+