Adjust admin documentation

docs/admin/40_preferences.rst

@@ -13,6 +13,9 @@ following preferences:
 * **Allow primary group owners to register future absences for students in their groups**:
   This allows owners of the student's primary group (e. g. the class)
   to register future absences like doctor's appointments or family celebrations.
+* **Grant the owner of a parent group the same privileges as the owners of the respective child groups**:
+  The owner of a group can perform all operations on child groups and related objects an owner of
+  the respected child groups is allowed to (e. g. editing the lesson documentation).
 * **Allow original teachers to edit their lessons although they are substituted:**
   In the case of substitute teaching, absent teachers can be given write-in privileges for the lesson.
 * **Carry over data from first lesson period to the following lesson periods in lessons over multiple periods:**