Add "secrets" example for service create API docs

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

api/swagger.yaml

@@ -7612,6 +7612,15 @@ paths:
                         Nameservers: ["8.8.8.8"]
                         Search: ["example.org"]
                         Options: ["timeout:3"]
+                      Secrets:
+                        -
+                          File:
+                            Name: "www.example.org.key"
+                            UID: "33"
+                            GID: "33"
+                            Mode: 384
+                          SecretID: "fpjqlhnwb19zds35k8wn80lq9"
+                          SecretName: "example_org_domain_key"
                     LogDriver:
                       Name: "json-file"
                       Options: