Discount code dashboard documentation (#147)

* Discount code dashboard documentation

Documentation for
reactioncommerce/reaction#1512 and
reactioncommerce/reaction#149

* lint updates

admin/discounts.md

@@ -0,0 +1,40 @@
+# Discounts
+Reaction has support for discount codes and discount rates.  A "code" is a code that can be applied during checkout that applies a discount to the cart subtotal.  A "rate" is a discount that is applied without needing a discount code to be applied.
+
+## Codes
+
+Discount codes can be enabled in the `Payments` settings in the Reaction dashboard.
+
+- `Discount Code`, case-sensitive string for a code
+- `Discount`, a discount formula value (string or number)
+- `Account Limit`, per user limit for this code
+- `Total Limit`, per code usage limit
+- `Calculation Method`
+  - credit - a credit is applied to the order subtotal up to the formula value
+  - discount - the formula value applied as a percentage discount off order subtotal
+  - sale - overrides item pricing with a fixed sale price
+  - shipping - the formula value should be a string that matches the name of a shipping method. The calculated shipping rate will be applied as a discount.
+
+![](/assets/admin-dashboard-payments-discounts.png "Payment Discounts")
+
+Discounts are validated when a user enters a code during checkout, and are applied as payment methods on the cart. The discount code usage is tracked once the order has been placed.
+
+## Rates
+
+> Rates are currently under development, and are not fully implemented.
+
+Rates are configured in the Catalog settings, and are used to apply discount pricing without requiring discount codes.
+
+![](/assets/admin-dashboard-payments-rates.png "Catalog Discount Rates")
+
+## Roadmap
+
+Updating rates and codes to use [conditional rules](https://github.com/reactioncommerce/reaction/issues/1663).
+
+Proposed conditional rules are:
+
+  - tags
+  - product / variant
+  - order value (min/max)
+  - start/end dates
+  - audience permissions

redoc.json

@@ -61,6 +61,12 @@
     "label": "Tax Calculations",
     "repo": "reaction-docs",
     "docPath": "admin/taxes.md"
+  }, {
+    "class": "guide-sub-nav-item",
+    "alias": "discounts",
+    "label": "Discounts",
+    "repo": "reaction-docs",
+    "docPath": "admin/discounts.md"
   }, {
     "class": "guide-sub-nav-item",
     "alias": "faqs",