Added mention to the PIM guide

Author: mnocon

docs/pim/pim_guide.md

@@ -105,6 +105,8 @@ Each customer group can have a default price discount that applies to all produc
 For example, you can offer a 10% discount for all products in the catalog to users who belong to the Resellers customer group.
 You can also set different prices for specific products or product variants for different customer groups.
 
+You can extend these capabilities even further by installing the [Discounts LTS Update](discounts_guide.md), available for [[= product_name_com =]].
+
 ### Product completeness
 
 Created product has its own list of the tasks required for product configuration: attributes, assets, content, prices, availability, and more.