add improved openapi frontmatter docs (#361)

api-playground/openapi/setup.mdx

@@ -104,24 +104,23 @@ reorder and add the files to your navigation manually.
 By using the OpenAPI reference, the name, description, parameters, responses,
 and the API playground will be automatically generated using the specifications.
 
-If you have multiple OpenAPI files, include the name of the OpenAPI file
-(without the file type `.json` or `.yaml`) to correctly map the information.
-This is not required if you have only one OpenAPI file - it will automatically
-detect your OpenAPI file.
+If you have multiple OpenAPI files, include the path to the OpenAPI file to map
+the MDX file to the appropriate OpenAPI file. This is not required if you have
+only one OpenAPI file - it will automatically detect your OpenAPI file.
 
 <CodeGroup>
 
 ```md Example
 ---
 title: "Get users"
-openapi: "openapi-1 GET /users"
+openapi: "/path/to/openapi-1.json GET /users"
 ---
 ```
 
 ```md Format
 ---
 title: "title of the page"
-openapi: openapi-file-name method path
+openapi: openapi-file-path method path
 ---
 ```