Document setting tick units

[etatara]

The RS GUI can show the tick value in different time units. We currently only document this via the Context XML loader mechanism, but can also be done via a ContextBuilder implementation via:

Quantity<?> x = Quantities.getQuantity(1, tech.units.indriya.unit.Units.DAY);
RunEnvironment.getInstance().getCurrentSchedule().setTimeQuantity(x);

Provide a short blurb in the user guide, FAQ, and one of the demo models.