docs: rearrange user guide (#2127)

* added lists guide

* restructure existing guides

* added new pages after restructuring

* added blank pages + rearranged sidebar

docs/content/user-guide/discounts/index.md

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+---
+sidebar_position: 1
+---
+
+# Discounts Overview
+
+In this document, you’ll get an overview of the customer listing page and everything you can do with it.
+
+## Overview
+
+You can create discounts of different types in Medusa that customers use on checkout:
+
+- **Percentage Discounts** to deduct a percentage of the total amount of an order.
+- **Fixed Discounts** to deduct a fixed amount from the total amount of an order.
+- **Free Shipping** to override the delivery amount of an order and make it free.
+
+Discounts are in the form of a code that your customers can use. You can set options for a discount such as a start and an end date.
+
+You can also specify conditions for discounts, such as applying them for specific products or shipping options.
+
+---
+
+## View List of Discounts
+
+You can view the list of available discounts in your ecommerce store by clicking on Discounts from the sidebar menu.
+
+In the list, you can see discount details such as the code, description, amount, and status.
+
+---
+
+## Learn More About Discounts
+
+- [Discount Conditions Overview](./conditions.md)
+- [Create a Discount](./create.md)
+- [Edit a Discount](./edit.md)