Update setup.mdx (#421)

Author: dino475

api-playground/openapi/setup.mdx

@@ -47,6 +47,9 @@ The fastest way to get started with OpenAPI is to add an `openapi` field to a ta
 
 ![](/images/autogeneration-with-tabs.png)
 
+<Tip>To validate your OpenAPI spec, you can use this command: <br/>`mintlify openapi-check <openapiFilenameOrUrl>`</Tip>
+
+
 When using this option, the metadata for the generated pages will have the following default values:
 
 * `title`: The `summary` field from the OpenAPI operation, if present. Otherwise a title generated from the HTTP method and endpoint.