Explain the order of where pytest-django finds DJANGO_SETTINGS_MODULE

This was changed before the 2.9.0 release and was not documented. The
change is backward incompatible and may surprise users.

Then change was originally made in #199.

docs/changelog.rst

@@ -30,6 +30,14 @@ Compatibility
 * Drop support for Django 1.3. While pytest-django supports a wide range of
   Django versions, extended for Django 1.3 was dropped in february 2013.
 
+* Settings defined in `pytest.ini`/`tox.ini`/`setup.cfg` used to override
+  `DJANGO_SETTINGS_MODULE` defined in the environment. Previously the order was
+  undocmented. Now, instead the settings from the environment will be used
+  instead. If you previously relied on overriding the enviornment variable, you
+  can instead specify `addopts = --ds=yourtestsettings` in the ini-file which
+  will use the test settings. See `PR #199
+  <https://github.com/pytest-dev/pytest-django/pull/199>`_.
+
 2.8.0
 -----
 

docs/configuring_django.rst

@@ -38,6 +38,12 @@ Example contents of pytest.ini::
     [pytest]
     DJANGO_SETTINGS_MODULE = test_settings
 
+Order of choosing settings
+--------------------------
+
+If `--ds`, the environment variable and the pytest.ini configuration is used at
+the same time, pytest-django will first prefer using settings from the command
+line option `--ds`, then the environment variable and last the pytest.ini.
 
 Using django-configurations
 ---------------------------