[ADD] manufacturing: How to manage BoMs for product variants

manufacturing/overview/bill_of_materials.rst

@@ -7,3 +7,4 @@ Bill of Materials
 
    getting_started/bill_configuration
    bill_of_materials/kit_shipping
+   bill_of_materials/product_variants

manufacturing/overview/bill_of_materials/product_variants.rst

@@ -0,0 +1,23 @@
+=======================================
+How to manage BoMs for product variants
+=======================================
+
+Odoo allows you to use one bill of materials for multiple variants of
+the same product. Simply enable variants from
+:menuselection:`Configuration --> Settings`.
+
+.. image:: media/product_variants01.png
+    :align: center
+
+You will then be able to specify which component lines are to be used in
+the manufacture of each product variant. You may specify multiple
+variants for each line. If no variant is specified, the line will be
+used for all variants.
+
+When defining variant BoMs on a line-item-basis, the **Product
+Variant** field in the main section of the BoM should be left blank.
+This field is used when creating a BoM for one variant of a product
+only.
+
+.. image:: media/product_variants02.png
+    :align: center