Add support for the customer parameter in the subscription list

docs/technical/interoptability/stripe/subscriptions.md

@@ -11,7 +11,7 @@ The Stripe Subscription Interopability layer is to allow you to continue using t
 
 | Name | Supported | Description |
 | --- | --- | --- |
-| customer | no | The ID of the customer whose subscriptions will be retrieved. |
+| customer | yes | The ID of the customer whose subscriptions will be retrieved. |
 | price | no  | Filter for subscriptions that contain this recurring price ID. |
 | status | no | The status of the subscriptions to retrieve. Passing in a value of canceled will return all canceled subscriptions, including those belonging to deleted customers. Pass ended to find subscriptions that are canceled and subscriptions that are expired due to incomplete payment. Passing in a value of all will return subscriptions of all statuses. If no value is supplied, all subscriptions that have not been canceled are returned. |
 | automatic_tax | no | Filter subscriptions by their automatic tax settings. |