doc: improved configuration documentation

doc/configuration.rst

@@ -4,14 +4,22 @@ Configuration
 pytest-iam can be configured by redefining or expanding the :meth:`~pytest_iam.iam_configuration` fixture.
 This returns a :const:`dict` containing the canaille :doc:`canaille:configuration`.
 
-   .. code:: python
+.. code-block:: python
 
     @pytest.fixture(scope="session")
     def iam_configuration(iam_configuration):
-        iam_configuration["ACL"]["DEFAULT"]["WRITE"].append("groups")
+        iam_configuration["CANAILLE"]["ACL"]["DEFAULT"]["WRITE"].append("groups")
         return iam_configuration
 
-The configuration will also be read:
+The configuration will also be read from a `.pytest-iam.env` file if existing.
 
-- from a `.pytest-iam.env` file if existing;
-- from any environment var with a valid Canaille setting name prefixed by `PYTEST_IAM_`.
+.. code-block:: bash
+   :caption: .pytest-iam.env
+
+    CANAILLE_OIDC__REQUIRE_NONCE=false
+
+It can also be read from any environment var with a valid Canaille setting name prefixed by `PYTEST_IAM_`.
+
+.. code-block:: bash
+
+    env PYTEST_IAM_CANAILLE_OIDC__REQUIRE_NONCE=false pytest