Help with auto moving script

I am new to scripting, and i don’t know much of it. I need help with making a Auto-Moving script. I am making a endless runner, and i made a script that makes my player go forward as it press W, using rigidbody. But, how can i make a script that makes the player go forward even if he is not pressing any key? Like a Auto-move.

This is my script:

using UnityEngine;
using System.Collections;

public class goahead : MonoBehaviour
{

    public float speed = 1f;

    void Update()
    {
        transform.Translate(Vector3.forward * Input.GetAxis("Vertical") * Time.deltaTime * speed);
    }
}

You would do something like this :

void Update()
{
    transform.position = transform.position + (transform.forward * speed * Time.deltaTime);
}