Document that cleanup doesn't work in acceptance tests

Re-submitting Codeception/Codeception#5734 and #1 - finally closing Codeception/Codeception#5286 now (I hope :-)

Author: ThomasLandauer

src/Codeception/Module/Doctrine2.php

@@ -60,8 +60,23 @@
  *
  * This will use static method of `MyDb::createEntityManager()` to establish the Entity Manager.
  *
- * By default, the module will wrap everything into a transaction for each test and roll it back afterwards. By doing this
- * tests will run much faster and will be isolated from each other.
+ * By default, the module will wrap everything into a transaction for each test and roll it back afterwards
+ * (this is controlled by the `cleanup` setting).
+ * By doing this, tests will run much faster and will be isolated from each other.
+ *
+ * To use the Doctrine2 Module in acceptance tests, set up your `acceptance.suite.yml` like this:
+ *
+ * ```yaml
+ * modules:
+ *     enabled:
+ *         - Symfony:
+ *             part: SERVICES
+ *         - Doctrine2:
+ *             depends: Symfony
+ * ``
+ *
+ * You cannot use `cleanup: true` in an acceptance test, since Codeception and your app (i.e. browser) are using two
+ * different connections to the database, so Codeception can't wrap changes made by the app into a transaction.
  *
  * ## Status
  *