Add triangles intro

osu.Game.Tests/Visual/Menus/TestSceneIntroTriangles.cs

@@ -0,0 +1,15 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using NUnit.Framework;
+using osu.Framework.Screens;
+using osu.Game.Screens.Menu;
+
+namespace osu.Game.Tests.Visual.Menus
+{
+    [TestFixture]
+    public class TestSceneIntroTriangles : IntroTestScene
+    {
+        protected override IScreen CreateScreen() => new IntroTriangles();
+    }
+}