Thank you works perfectly

var projectile : Rigidbody;
var speed = 50;

var fireRate = 0.11;
private var lastShot = -10.0;//Dont touch!

function Update () {
    if(Time.time > fireRate+lastShot){
        clone = Instantiate(projectile, transform.position, transform.rotation);
        projectile.tag = "Bullet";
        clone.velocity = transform.TransformDirection( Vector3 (0, 0, speed));

        lastShot = Time.time;
    }
Destroy(clone.gameObject, 3);
}

You use a simple if statement to check if a certain time has passed so we can fire again.