docs(readme): add webhook usage examples

Author: rnegron

README.md

@@ -22,7 +22,6 @@ A modern, type-safe Python library for the ATH Móvil payment platform.
 - Pydantic data validation
 - Automatic retries with exponential backoff
 - Comprehensive error handling
-- High test coverage
 
 ## Installation
 
@@ -67,7 +66,7 @@ print(f"Payment completed: {payment_result.data.reference_number}")
 
 # Refund the payment (requires a client initialized with private token)
 refund_result = client.refund_payment(
-    reference_number=payment_result.data.reference_number,,
+    reference_number=payment_result.data.reference_number,
     amount="5.00",
 )
 ```
@@ -123,6 +122,57 @@ with ATHMovilClient(public_token="token") as client:
     # Client is automatically closed when exiting the context
 ```
 
+## Webhooks
+
+Subscribe to real-time transaction notifications:
+
+```python
+# Subscribe to webhooks (requires private token)
+client = ATHMovilClient(
+    public_token="your_public_token",
+    private_token="your_private_token",
+)
+
+client.subscribe_webhook(
+    listener_url="https://yoursite.com/webhook",
+    payment_received_event=True,
+    refund_sent_event=True,
+    ecommerce_payment_received_event=True,
+    ecommerce_payment_cancelled_event=True,
+    ecommerce_payment_expired_event=True,
+)
+```
+
+Parse incoming webhook payloads in your endpoint:
+
+```python
+from athm.webhooks import parse_webhook, WebhookEventType, WebhookStatus
+
+@app.post("/webhook")
+async def handle_webhook(request: Request):
+    payload = await request.json()
+    event = parse_webhook(payload)
+
+    if event.status == WebhookStatus.COMPLETED:
+        if event.transaction_type == WebhookEventType.PAYMENT:
+            # Standard payment completed
+            print(f"Payment received: {event.reference_number} for ${event.total}")
+        elif event.transaction_type == WebhookEventType.ECOMMERCE:
+            # eCommerce payment completed
+            print(f"Order {event.ecommerce_id} completed: ${event.total}")
+        elif event.transaction_type == WebhookEventType.REFUND:
+            # Refund processed
+            print(f"Refund sent: {event.reference_number}")
+
+    elif event.status == WebhookStatus.CANCELLED:
+        print(f"Transaction cancelled: {event.ecommerce_id}")
+
+    elif event.status == WebhookStatus.EXPIRED:
+        print(f"Transaction expired: {event.ecommerce_id}")
+
+    return {"status": "ok"}
+```
+
 ## Documentation
 
 - [Full Documentation](https://athm-python.readthedocs.io)