chore(changelog): add link to example usage

Author: mharrisb1

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 Adds `router` property on `OpenAIMock` class to expose instance of [respx.MockRouter](https://github.com/lundberg/respx/blob/366dd0bea824464e6ec9242a88f9b390a9dd74cb/respx/router.py#L323) to easily allow user to add additional routes to mock like non-OpenAI API calls, or enable a call to a route to pass through to the external service.
 
+Usage example can be found [here](https://github.com/mharrisb1/openai-responses-python/blob/main/examples/test_router_usage.py).
+
 Closed:
 
 - [#36: feat(api): expose RESPX router as property](https://github.com/mharrisb1/openai-responses-python/issues/36)