added .coveragerc to readme repo structure list

Author: pavelkomarov

README.md

@@ -92,6 +92,7 @@ Much more extensive usage is demonstrated in Jupyter notebooks:
 - `docs/` contains `make` files and `.rst` files to govern the way `sphinx` builds documentation, either locally by navigating to this folder and calling `make html` or in the cloud by `readthedocs.io`.
 - `examples/` contains Jupyter notebooks that demonstrate some usage of the library.
 - `pynumdiff/` contains the source code. For a full list of modules and further navigation help, see the readme in this subfolder.
+- `.coveragerc` governs `coverage` runs, listing files and functions/lines that should be excluded, e.g. plotting code.
 - `.editorconfig` ensures tabs are displayed as 4 characters wide.
 - `.gitignore` ensures files generated by local `pip install`s, Jupyter notebook runs, caches from code runs, virtual environments, and more are not picked up by `git` and accidentally added to the repo.
 - `.pylintrc` configures `pylint`, a tool for autochecking code quality.