public class WelcomeTextController : MonoBehaviour
{
    public Text text;
    public float typingDuration;

    [TextArea(10, 10)]
    public string welcomeText;

    void Start()
    {
        new Interpolation(t => SetString(str, ratio))
            .Duration(typingDuration)
            .Build(this)
            .Play();
    }

    void SetString(string str, float ratio)
    {
        this.text.text = str.Substring(0, (int) (ratio * str.Length)));
    }
}