feat: payments system configuration docs

docs/INSTALL.md

@@ -42,3 +42,33 @@ HOSTEA = {
     },
 }
 ```
+
+## Payments
+
+At present, we rely on [Stripe](https://stripe.com) for processing
+payments. So we are limited to the countries at which Stripe operates.
+
+To deploy payments, please configure the options in settins.py that
+start with `PAYMENT_*`
+
+**NOTE: Please don't change the `PAYMENT_MODEL`. Changing it will
+break the app**
+
+```python
+## django-payments configuration
+
+PAYMENT_MODEL = "billing.Payment" # please don't change this value
+ # the URL at which Dashbaord will be listening
+PAYMENT_HOST = "http://localhost:8000"
+PAYMENT_VARIANTS = {
+    "stripe": (
+        "payments.stripe.StripeProvider",
+        {
+			# stripe API secret key, available in Stripe dashboard
+            "secret_key": env.get_value("STRIPE_SECRET_KEY"),
+			# stripe API public key, available in Stripe dashboard
+            "public_key": env.get_value("STRIPE_PUBLIC_KEY"),
+        },
+    )
+}
+```