[#66] update documentation

docs/installation/config.rst

@@ -80,6 +80,7 @@ Optional
 * ``LOG_LEVEL``: control the verbosity of logging output. Available values are ``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO`` and ``DEBUG``. Defaults to: ``WARNING``.
 * ``LOG_QUERIES``: enable (query) logging at the database backend level. Note that you must also set ``DEBUG=1``, which should be done very sparingly!. Defaults to: ``False``.
 * ``LOG_REQUESTS``: enable logging of the outgoing requests. Defaults to: ``False``.
+* ``SESSION_COOKIE_AGE``: For how long, in seconds, the session cookie will be valid. Defaults to: ``1209600``.
 * ``SESSION_COOKIE_SAMESITE``: The value of the SameSite flag on the session cookie. This flag prevents the cookie from being sent in cross-site requests thus preventing CSRF attacks and making some methods of stealing session cookie impossible.Currently interferes with OIDC. Keep the value set at Lax if used. Defaults to: ``Lax``.
 * ``CSRF_COOKIE_SAMESITE``: The value of the SameSite flag on the CSRF cookie. This flag prevents the cookie from being sent in cross-site requests. Defaults to: ``Strict``.
 * ``ENVIRONMENT``: An identifier for the environment, displayed in the admin depending on the settings module used and included in the error monitoring (see ``SENTRY_DSN``). The default is set according to ``DJANGO_SETTINGS_MODULE``.