Note on demo session

src/main/resources/arsnova.properties.example

@@ -213,6 +213,9 @@ question.answer-option-limit=8
 question.parse-answer-option-formatting=true
 
 # Demo session id to show above session login button
+# You can freely use the demo session of arsnova.eu/mobile 
+# which can be imported from the repro:
+# https://github.com/thm-projects/arsnova-mobile/tree/master/demo-sessions
 session.demo-id=
 
 # Label underneath ARSnova logo
@@ -280,4 +283,4 @@ pp.session-levels.en = General Education,\
 #
 tracking.provider=piwik
 tracking.tracker-url=
-tracking.site-id=
+tracking.site-id=
\ No newline at end of file