Leave the last vehicle's coupler at 0 so the train gets its end signals

The simulator hangs end signals only on a last vehicle with coupler 0; every
new car came with 3 and the pass that couples neighbours never touched the
last one, nor did taking a car off the end. The coupler editor says so for
the last vehicle.

StarterNG/startercfg/lang/en.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Split the unit into individual cars</String>
     <String key="AppliesToUnit">Shared by the whole unit</String>
     <String key="CouplingUnitRear">Coupler at the rear of the unit</String>
+    <String key="CouplingLastNote">Last vehicle: coupler 0 gets the end signals. Any other code couples the train to whatever stands behind it, and the simulator puts up no end signals.</String>
     <String key="Join">Join</String>
     <String key="TipJoin">Couple this vehicle with the next one into a single unit</String>
     <String key="TipReorder">Drag to reorder</String>