fix: following Chris's review (added unittest to README.md)

Author: f-allian

README.md

@@ -112,7 +112,7 @@ To contribute to our work, please ensure the following:
 3. [Push your changes](https://docs.github.com/en/get-started/using-git/pushing-commits-to-a-remote-repository) to your new branch in your remote fork, compare with `CausalTestingFramework/main`, and ensure any conflicts are resolved.
 4. Create a draft [pull request](https://docs.github.com/en/get-started/quickstart/hello-world#opening-a-pull-request) from your branch, and ensure you have [linked](https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/autolinked-references-and-urls) it to any relevant issues in your description. 
 
-We use the [pytest](https://pytest.org/en/latest/) framework as our testing suite, [pylint](https://pypi.org/project/pylint/) for our code analyser, and [black](https://pypi.org/project/black/) for our code formatting.
+We use the [unittest]() module to develop our tests and the [pytest](https://pytest.org/en/latest/) framework as our test discovery, [pylint](https://pypi.org/project/pylint/) for our code analyser, and [black](https://pypi.org/project/black/) for our code formatting.
 To find the other (optional) developer dependencies, please check `pyproject.toml`.