Add section for pytest-recording plugin in CONTRIBUTING.md

* **Plugin usage**: Add a section explaining the use of `pytest-recording` plugin for creating VCR cassettes.
* **Recording instructions**: Provide instructions on how to record a new VCR cassette using `uv run pytest --record-mode=once tests/desired_test_module.py`.
* **Configuration links**: Link to the configuration in `tests/conftest.py` and the cassettes in `tests/cassettes`.
* **Header removals**: Document header removals from responses to exclude sensitive information.
* **Size comment**: Add a comment about keeping the cassettes less than 1 MB in size.

CONTRIBUTING.md

@@ -52,6 +52,27 @@ Use the following commands:
 
 See our GitHub Actions [`tests.yml`](.github/workflows/tests.yml) for further reference.
 
+## Using `pytest-recording` and VCR cassettes
+
+We use the [`pytest-recording`](https://github.com/kiwicom/pytest-recording) plugin
+to create VCR cassettes to cache HTTP requests,
+making our unit tests more deterministic.
+
+To record a new VCR cassette:
+
+```bash
+uv run pytest --record-mode=once tests/desired_test_module.py
+```
+
+And the new cassette(s) should appear in [`tests/cassettes`](tests/cassettes).
+
+Our configuration for `pytest-recording` can be found in [`tests/conftest.py`](tests/conftest.py).
+This includes header removals (e.g. OpenAI `authorization` key)
+from responses to ensure sensitive information is excluded from the cassettes.
+
+Please ensure cassettes are less than 1 MB
+to keep tests loading quickly.
+
 ## Additional resources
 
 For more information on contributing, please refer to the [CONTRIBUTING.md](CONTRIBUTING.md) file in the repository.