[wpilib] Update MotorControllerGroup deprecation message (#6171)

The current message could be read as encouraging the use of CAN motor
controllers. This tries to make it more clear.

wpilibc/src/main/native/include/frc/motorcontrol/MotorControllerGroup.h

@@ -21,8 +21,8 @@ namespace frc {
  * Allows multiple MotorController objects to be linked together.
  */
 class [[deprecated(
-    "Use CAN motor controller followers or "
-    "PWMMotorController::AddFollower()")]] MotorControllerGroup
+    "Use PWMMotorController::AddFollower() or if using CAN motor controllers,"
+    "use their method of following.")]] MotorControllerGroup
     : public wpi::Sendable,
       public MotorController,
       public wpi::SendableHelper<MotorControllerGroup> {