add welcome menu

Assets/Loader.cs

@@ -61,13 +61,17 @@ public class Loader : MonoBehaviour {
     public void NextScene() {
         int current = scene.buildIndex;
         int next = (current + 1) % (SceneManager.sceneCountInBuildSettings);
+
+        // welcome is at 0. skip it
+        if (next == 0) next = 1;
         if (next != current) LoadScene(next);
     }
 
     public void PrevScene() {
         int current = scene.buildIndex;
         int prev = (current - 1);
-        if (prev < 0) prev = SceneManager.sceneCountInBuildSettings - 1;
+        // check for welcome
+        if (prev <= 0) prev = SceneManager.sceneCountInBuildSettings - 1;
         if (prev != current) LoadScene(prev);
     }