better messaging on handling of unknown functions. fixes #606

docs/scarpet/api/Auxiliary.md

@@ -444,6 +444,9 @@ algorithm has taken in to account last time mobs spawned.
 Schedules a user defined function to run with a specified `delay` ticks of delay. Scheduled functions run at the end 
 of the tick, and they will run in order they were scheduled.
 
+In case you want to schedule a function that is not defined in your module, please read the tips on
+ "Passing function references to other modules of your application" section in the `call(...)` section.
+
 ### `statistic(player, category, entry)`
 
 Queries in-game statistics for certain values. Categories include: