How can i get my projectile to face its direction of travel?

i know there are many questions similar to this, but none of the solutions have worked for me after 6 hours of searching. also im working in unity 5, which changes some things. basically i just want my projectile (which resembles a pill) to point in the direction its travelling. it moves to my mouse cursor when i click. this is my code so far:

note: the transform.rotation line comes up with a "an object referance is required for the non-static..." error.

private Rigidbody2D myRigidbody;

 void Start()
 {
     camera = (Camera)GameObject.FindObjectOfType(typeof(Camera)); // get the camera

     myRigidbody = GetComponent<Rigidbody2D>();

     // get world location of click
     clickPos = camera.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, Input.mousePosition.z));

     

     Destroy(gameObject, 3); // give projectile 3 seconds lifetime, if they aren't already destroyed

     transform.rotation = Quaternion.SetLookRotation(myRigidbody.velocity);


 }

 void Update()
 {
     transform.position = Vector2.MoveTowards(transform.position, clickPos, speed * Time.deltaTime);

     Debug.Log("cursor pos" + clickPos);
     //Vector2 motionDirection = myRigidbody.velocity.normalized;


     if(((Vector3)transform.position == clickPos))
     {
         Destroy(gameObject);
     }