Update setup.mdx (#334)

I changed endpoint to path after Hahnbee and I agreed it should say path not endpoint.

api-playground/openapi/setup.mdx

@@ -121,7 +121,7 @@ openapi: "openapi-1 GET /users"
 ```md Format
 ---
 title: "title of the page"
-openapi: openapi-file-name method endpoint
+openapi: openapi-file-name method path
 ---
 ```