feat: add menu scene + select level scene + nav between them (#31)

Assets/MainMenu.cs

@@ -0,0 +1,20 @@
+using UnityEngine;
+using UnityEngine.SceneManagement;
+
+public class MainMenu : MonoBehaviour
+{
+    public void LaunchGame()
+    {
+        SceneManager.LoadSceneAsync(1);
+    }
+
+    public void OpenSettings()
+    {
+        // SceneManager.LoadSceneAsync(?);
+    }
+
+    public void QuitGame()
+    {
+        Application.Quit();
+    }
+}