Face Direction Movement using CharacterController

Hi to all! I have a simple question about how rotate the character to face his movement direction.

It's a isometric project that uses CharacterController.Move script reference to move the player.

Ps.: is NOT a click-to-move or mouse pointer direction like most Survival-games, just a simple WASD/Joystick Axis based, and the camera is fixed too.

 public class ExampleClass : MonoBehaviour {
     public float speed = 6.0F;
     public float jumpSpeed = 8.0F;
     public float gravity = 20.0F;
     private Vector3 moveDirection = Vector3.zero;
     void Update() {
         CharacterController controller = GetComponent<CharacterController>();
         if (controller.isGrounded) {
             moveDirection = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
             moveDirection = transform.TransformDirection(moveDirection);
             moveDirection *= speed;
             if (Input.GetButton("Jump"))
                 moveDirection.y = jumpSpeed;            
         }
         moveDirection.y -= gravity * Time.deltaTime;
         controller.Move(moveDirection * Time.deltaTime);
     }
 }

How can I implement the rotation on Y-axis in this case and make the character face his direction??

Thanks for the attention!