Add comment to OI saying to maintain controllers.txt

Author: Gabe-Mitnick

Robot2018/src/org/usfirst/frc/team199/Robot2018/OI.java

@@ -32,6 +32,10 @@
  * interface to the commands and command groups that allow control of the robot.
  */
 public class OI {
+	/*
+	 * WHENEVER YOU ADD OR CHANGE WHAT A BUTTON OR JOYSTICK DOES, indicate in
+	 * /docs/controllers.txt to keep that reference up to date.
+	 */
 
 	public Joystick leftJoy;
 	private JoystickButton shiftLowGearButton;