We ned to install ruff for the pre-commit hook

doc/development.rst

@@ -14,6 +14,13 @@ We can install ``pre-commit`` with `pipx <https://pipx.pypa.io/stable/>`__, and
 
    .. literalinclude:: ../.pre-commit-config.yaml
 
+In the pre-commit hook we run the `ruff <https://docs.astral.sh/ruff/>`__ linter and code formatter.
+It can be installed with ``pipx``:
+
+.. code-block:: sh
+
+   pipx install ruff
+
 We also use the `nox automation tool <https://nox.thea.codes/en/stable/>`__ to run test cases with `pytest <https://docs.pytest.org/>`__, and to format and lint code with `ruff <https://docs.astral.sh/ruff/>`__.
 We can install ``nox`` with ``pipx``: