Add basic intro countdown and game states

Assets/Scripts/UI/GameStartCountdownUI.cs

@@ -0,0 +1,45 @@
+using System.Collections;
+using System.Collections.Generic;
+using TMPro;
+using UnityEngine;
+
+public class GameStartCountdownUI : MonoBehaviour
+{
+
+    [SerializeField] private TextMeshProUGUI countdownText;
+
+    private void Start()
+    {
+        GameStateManager.Instace.OnStateChanged += GameStateManager_OnStateChanged;
+
+        Hide();
+    }
+
+    private void GameStateManager_OnStateChanged(object sender, System.EventArgs e)
+    {
+        
+        if (GameStateManager.Instace.IsCountdownToStartActive())
+        {
+            Show();
+        } else
+        {
+            Hide();
+        }
+
+    }
+
+    private void Update()
+    {
+        countdownText.text = Mathf.Ceil(GameStateManager.Instace.GetCountdownToStartTimer()).ToString();
+    }
+
+    private void Show()
+    {
+        gameObject.SetActive(true);
+    }
+
+    private void Hide()
+    {
+        gameObject.SetActive(false);
+    }
+}