Reading from .txt file c#

Hi I am attempting to write a script to create a gui box with text in it that changes based on a keyboard click. I have got the basics up and running (its far from the finnished product). I am haveing an issue wuth this section of code.

    void read_file()
    {
           
                TextReader tr = new StreamReader("Assets/test.txt");
                
                conversation = tr.ReadLine();
                tr.Close();
    }

when I am running the script in unity it will locate the txt file and read the first line to the variable and then update my GUI element. but when I buiold the project and test it it does not work so I assume it cannot be located. I would appriciate any advice on this issue. Here is the full script I have coded so far if it helps for refrence.

using UnityEngine;
using System.Collections;
using System;
using System.IO;

public class convo : MonoBehaviour {
    public string conversation;

	// Use this for initialization
	void Start () {
        conversation = "Hello this is a test";
	
	}
	
	// Update is called once per frame
	void Update () {

        if (Input.GetKeyUp(KeyCode.E))
            {
                read_file();
            }
	
	}
    void OnGUI()
    {
        GUI.Box(new Rect(10, 200, 500, 50), conversation);
    }
    void read_file()
    {
           
                TextReader tr = new StreamReader("Assets/test.txt");
                
                conversation = tr.ReadLine();
                tr.Close();
    }
}

Thanks

Dave

You will need to create an Assets folder with the a copy of the txt in the build path.

Thanks a lot for the help this has really been annoying me. gonna try it soon as I get home.

Thanks you all!!