docs: add example OpenAPI spec to SDK quickstart pages (#5602)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Devin Logan <devinannlogan@gmail.com>

Author: devin-ai-integration[bot]

fern/products/sdks/snippets/init-fern-folder.mdx

@@ -24,6 +24,10 @@
   fern init --openapi https://api.example.com/openapi.yml \
   --organization <YourOrganization>
   ```
+  ```bash title="Example (Petstore)"
+  fern init --openapi https://petstore3.swagger.io/api/v3/openapi.json \
+  --organization my-org
+  ```
 </CodeBlocks>
 
   <Tip>