add note on using Nix shell with Nox and pytest

README.md

@@ -19,3 +19,12 @@ This project is configured to use Nix for a shell/environment with dependencies,
 1. Exit Nix shell: `Ctrl-d`
 1. Restart Nix shell: `shell.nix`
 
+### Testing
+From the Nix shell, run `nox --list` to see a list of available commands, notably to run tests against different versions of Python, to reformat code to be style-compliant, and to run the linter.
+
+NB: To pass arguments through `nox` to `pytest`, separate the argument strings with `--`, e.g.:
+```shell
+nox -s tests-3.12 -- -vv
+```
+to run the tests with additional verbosity (e.g., `pytest -vv`)
+