[Docs] Add references

docs/admin/10_features.rst

@@ -7,7 +7,7 @@ functionality to automatically import data from Untis into data models
 of the core and `Chronos`, the timetable and substitution app of AlekSIS.
 
 Currently, we only support importing data from the MySQL database of
-`Untis MultiUser`. This is done through configurable background tasks
+`Untis MultiUser`_. This is done through configurable background tasks
 which are executed in a specific interval or at specific points in time.
 
 Supported Untis features
@@ -34,3 +34,5 @@ Currently, the following features are known not to be supported:
 * Prebookings
 * Statistical data
 * Special rooms (subject and group rooms)
+
+.. _Untis MultiUser: https://www.untis.at/produkte/untis-das-grundpaket/multiuser