more payments docs updates

packages/vulcan-payments/README.md

@@ -2,30 +2,18 @@
 
 This package helps you process charges with Vulcan. It currently only supports Stripe, but other payment processors may be supported in the future (PRs welcome!). 
 
-### Overview
+## Overview
 
 This package does the following things: 
 
 - Provide a button that triggers the [Stripe Checkout](https://stripe.com/checkout) form.
-- Once the form is submitted, trigger a GraphQL mutation that will perform the charge. 
-- The mutation then returns a document associated with the charge. 
+- Once the form is submitted, trigger a GraphQL mutation that will:
+  - Perform the charge.
+  - Create a new Charge.
+  - Modify a document associated with the charge.
+- The mutation then returns a document associated with the charge to the client.
 
-### Charges
-
-Charges are stored in the database with the following fields:
-
-- `_id`: the charge's id. 
-- `createdAt`: the charge's timestamp.
-- `userId`: the Vulcan `_id` of the user performing the purchase. 
-- `tokenId`: the charge token's id. 
-- `productKey`: the key corresponding to the product being purchased, as defined with `addProduct`.
-- `type`: the type of charge (currently only `stripe` is supported).
-- `test`: whether the operation is a test or not. 
-- `data`: a JSON object containing all charge data generated by the payment processor.
-- `properties`: a JSON object containing any custom properties passed by the client. 
-- `ip`: the IP address of the client performing the purchase. 
-
-### Settings
+## Settings
 
 Stripe requires the following public setting in your `settings.json`. 
 
@@ -49,7 +37,22 @@ As well as the following private setting (can be stored in the setting's root or
 }
 ```
 
-### Products
+## Charges
+
+Charges are stored in the database with the following fields:
+
+- `_id`: the charge's id. 
+- `createdAt`: the charge's timestamp.
+- `userId`: the Vulcan `_id` of the user performing the purchase. 
+- `tokenId`: the charge token's id. 
+- `productKey`: the key corresponding to the product being purchased, as defined with `addProduct`.
+- `type`: the type of charge (currently only `stripe` is supported).
+- `test`: whether the operation is a test or not. 
+- `data`: a JSON object containing all charge data generated by the payment processor.
+- `properties`: a JSON object containing any custom properties passed by the client. 
+- `ip`: the IP address of the client performing the purchase. 
+
+## Products
 
 A product is a type of purchase a user can make. It has a `name`, `amount` (in cents), `currency`, and `description`.
 
@@ -80,7 +83,7 @@ addProduct('book', book => ({
 
 Make sure you define your products in a location accessible to both client and server, in order to access them both on the front-end to configure Stripe Checkout, and in the back-end to perform the actual charge. 
 
-### Checkout Component
+## Checkout Component
 
 ```js
 <Components.Checkout 
@@ -101,21 +104,42 @@ Make sure you define your products in a location accessible to both client and s
 - `fragmentName`: a registeredGraphQL fragment name.
 - `properties`: any other properties you want to pass on to `createChargeMutation` on the server. 
 
-### Associating a Collection Document
+## Associating a Collection Document
 
 The Vulcan Charge package requires associating a document with a purchase, typically the item being paid for. For example, maybe you want people to buy access to a file hosted on your servers, and give them download access once the transaction is complete. 
 
-The `associatedCollection` and `associatedId` props give you an easy way to implement this by automatically setting a `chargeId` field on the document once the charge succeeds. 
+The `associatedCollection` and `associatedId` props give you an easy way to implement this by automatically setting a `chargeIds` field on the document once the charge succeeds. 
 
 For example, if you pass `associatedCollection={Jobs}` and `associatedId="foo123"` to the Checkout component, the resulting charge's `_id` will automatically be added to a `chargeIds` array on job `foo123`. 
 
 The `createChargeMutation` GraphQL mutation will then return that job according to the `fragment` property specified. 
 
-### The Chargeable Type
+Note: you will need to make sure that your collection accepts this `chargeIds` field. For example:
 
-In order to be able to return any associated document, the package creates a new `Chargeable` type that is an union of every chargeable collection's types. 
+```js
+Jobs.addField([
+  {
+    fieldName: 'chargeIds',
+    fieldSchema: {
+      type: Array,
+      optional: true,
+    }
+  },
+  {
+    fieldName: 'chargeIds.$',
+    fieldSchema: {
+      type: String,
+      optional: true,
+    }
+  }
+]);
+```
 
-### Post-Charge Updates
+#### The "Chargeable" Type
+
+In order to be able to return any associated document, the package creates a new `Chargeable` GraphQL type that is an union of every collection's types. 
+
+## Post-Charge Updates
 
 The best way to update a document based on a successful charge is by using the `collection.charge.sync` callback.