[Docs] Update information on usage for preferences

docs/admin/20_configuration.rst

@@ -67,8 +67,15 @@ The way data are imported can be configured from the menu under
   existing rooms if Untis has different data.
 * **Update existing supervision areas:** This will update the values of
   already existing supervision areas if Untis has different data.
-* **Use course groups:** This will build or search course groups (groups
+* **Use course groups:** This will search course groups (groups
   for each subject in a class) instead of setting the classes as groups.
+* **Create non-existing course groups**: In combination with _Use course groups_ being enabled,
+  this will create new course groups if no matching group was found.
+* **Register a data problem if a course group has been not found:** When this is activated,
+  the import will register a data problem if no matching course group was found,
+  independent of whether a new course group was created or not.
+* **Ignore incomplete substitutions**: If this is activated, Untis won't import any substitutions
+  which are not cancelled or without a new room, new teacher or new subject .
 
 Scheduling import tasks
 -----------------------