add .coveragerc example

.. _pytest: https://docs.pytest.org/en/7.1.x

.. _coverage: https://coverage.readthedocs.io/en/6.5.0/

Exclude files

-------------

To exclude specific files from coverage report, write a `.coveragerc` file.

.. code-block::

    [run]

    omit =

        # omit anything in a .local directory anywhere

        */.local/*

        # omit everything in /usr

        /usr/*

        # omit this single file

        utils/tirefire.py

An example `.coveragerc` for `csst_proto` is

.. code-block::

    [run]

    omit =

        tests/*

        setup.py

        csst_proto/top_level_interface.py

        test_codestyle.py

Conventions

-----------