[ADD] purchase: How to trigger a warning when purchasing at a specific vendor?

https://docs.google.com/document/d/1uGZ9u2a8I-Rj0B7gY-RAsbq1rXJn_X225afJNSNBnH4/edit?usp=sharing

purchase/replenishment/flows/warning_triggering.rst

@@ -2,4 +2,90 @@
 How to trigger a warning when purchasing at a specific vendor?
 ==============================================================
 
-*Coming soon...*
+Overview
+========
+
+The **Warning Messages and Alerts** module allow you to configure alerts
+on the customers and vendors or products.
+
+You can select the following types of warnings and create different
+warnings for purchases and sales:
+
+-   Warning: This option displays the warning message during the process, 
+    but allows the user to continue.
+
+-   Blocking Message: The message displays a warning message, but the 
+    user cannot continue the process further.
+
+Configuration
+=============
+
+Module Installation
+-------------------
+
+First, you need to install the **Warning Messages and Alerts** module. Go
+to **Apps** and look for it (don't forget to remove the **Apps** filter).
+
+.. image:: media/warning_triggering01.png
+    :align: center
+
+Vendor or Customer warnings
+---------------------------
+
+Go to :menuselection:`Purchases --> Vendors` or to :menuselection:`Sales --> Customers`.
+
+Open the vendor or the customer and click on the **Warnings** tab.
+
+.. image:: media/warning_triggering02.png
+    :align: center
+
+The available warnings are:
+
+-  Warning on the **Sales Order**
+
+-  Warning on the **Purchase Order**
+
+-  Warning on the **Picking**
+
+-  Warning on the **Invoice**
+
+Product Warnings
+----------------
+
+Go to :menuselection:`Purchases --> Products` or to :menuselection:`Sales --> Products`.
+
+Open the product and click on the **Notes** tab.
+
+.. image:: media/warning_triggering03.png
+    :align: center
+
+The available warnings are:
+
+-  Warning when selling this product.
+
+-  Warning when Purchasing this product.
+
+How to trigger a warning when purchasing at a specific vendor?
+==============================================================
+
+Go to the Purchases application, click on :menuselection:`Purchase --> Vendors`. 
+Go to the **Warnings** tab.
+
+Under **Warning on the Purchase Order**, choose **Warning** and write your
+warning.
+
+.. image:: media/warning_triggering04.png
+    :align: center
+
+Create a **Request for Quotation**. Go to 
+:menuselection:`Purchase --> Request for Quotation` and click on **Create**. 
+Choose the vendor on which a warning was set.
+
+When choosing the vendor, the warning will appear.
+
+.. image:: media/warning_triggering01.png
+    :align: center
+
+.. note::
+    If you set a blocking message instead of a warning message, you
+    won't be able to choose the vendor.