Add missing documentation for set_line

advtrains_luaautomation/README.txt

@@ -126,6 +126,8 @@ atc_set_text_outside(text)
 	Set text shown on the outside of the train. Pass nil to show no text.
 atc_set_text_inside(text)
 	Set text shown to train passengers. Pass nil to show no text.
+set_line(number)
+	Only for subway wagons: Display a line number (1-9) on the train.
 
 # Operator panel
 This simple node executes its actions when punched. It can be used to change a switch and update the corresponding signals or similar applications.