Updates docs

Signed-off-by: Somtochi Onyekwere <somtochionyekwere@gmail.com>

docs/spec/v1beta1/receiver.md

@@ -182,6 +182,23 @@ spec:
       name: webapp
 ```
 
+### Quay receiver
+
+```yaml
+apiVersion: notification.toolkit.fluxcd.io/v1beta1
+kind: Receiver
+metadata:
+  name: quay-receiver
+  namespace: default
+spec:
+  type: quay
+  secretRef:
+    name: webhook-token
+  resources:
+    - kind: ImageRepository
+      name: webapp
+```
+
 ### Generic receiver
 
 ```yaml

internal/server/receiver_handlers.go

@@ -183,7 +183,7 @@ func (s *ReceiverServer) validate(ctx context.Context, receiver v1beta1.Receiver
 
 		var p payload
 		if err := json.NewDecoder(r.Body).Decode(&p); err != nil {
-			return fmt.Errorf("cannot decode DockerHub webhook payload")
+			return fmt.Errorf("cannot decode Quay webhook payload")
 		}
 
 		s.logger.Info(