docs: add missing status property to Webhook docs (#647)

docs/webhooks.md

@@ -8,15 +8,16 @@ description: >-
 To get the latest status of your swaps, you can poll the status endpoints of the
 REST API, subscribe to the WebSocket, or set a webhook when creating the swap.
 
-To register a webhook add the following object to the request that creates the
+To register a webhook, add the following object to the request that creates the
 swap:
 
 ```json
 {
   ...
   "webhook": {
     "url": "<URL that should called>",
-    "hashSwapId": false
+    "hashSwapId": false,
+    "status": ["invoice.pending", "transaction.claim.pending"]
   }
 }
 ```
@@ -39,3 +40,6 @@ to false. When it is explicitly set to `true`, the swap id is hashed with SHA256
 and encoded as HEX in the webhook call. That is useful when the webhook is
 processed by a third party to which you do not want to leak information about
 your swaps.
+
+`status` is optional and is a list of swap status update events for which the
+webhook should be called. If not set, the webhook will be called for all events.