Clarify supported testing frameworks

Document that Test Explorer supports unittest and pytest while keeping the unsupported-framework guidance concise.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: eleanorjboyd

README.md

@@ -94,7 +94,7 @@ Learn more about the rich features of the Python extension:
 -   [Linting](https://code.visualstudio.com/docs/python/linting): Get additional code analysis with Pylint, Flake8 and more.
 -   [Code formatting](https://code.visualstudio.com/docs/python/formatting): Format your code with black, autopep or yapf.
 -   [Debugging](https://code.visualstudio.com/docs/python/debugging): Debug your Python scripts, web apps, remote or multi-threaded processes.
--   [Testing](https://code.visualstudio.com/docs/python/unit-testing): Run and debug tests through the Test Explorer with unittest or pytest.
+-   [Testing](https://code.visualstudio.com/docs/python/unit-testing): Run and debug `unittest` and `pytest` tests through the Test Explorer. Other frameworks, including `behave`, are not currently supported in the Test Explorer.
 -   [Jupyter Notebooks](https://code.visualstudio.com/docs/python/jupyter-support): Create and edit Jupyter Notebooks, add and run code cells, render plots, visualize variables through the variable explorer, visualize dataframes with the data viewer, and more.
 -   [Environments](https://code.visualstudio.com/docs/python/environments): Automatically activate and switch between virtualenv, venv, pipenv, conda and pyenv environments.
 -   [Refactoring](https://code.visualstudio.com/docs/python/editing#_refactoring): Restructure your Python code with variable extraction and method extraction. Additionally, there is componentized support to enable additional refactoring, such as import sorting, through extensions including [isort](https://marketplace.visualstudio.com/items?itemName=ms-python.isort) and [Ruff](https://marketplace.visualstudio.com/items?itemName=charliermarsh.ruff).