Add more details about 3D triangle demo

index.html

@@ -23,6 +23,7 @@
     <canvas id="app-squish"></canvas>
 
     <h2 id="demo-triangle3d"><a href="#demo-triangle3d">Triangle 3D</h2>
+    Rotating rainbow triangle in 3D. Unlike <a href="#demo-3d">3D dots above</a> this is a solid shape. Source:&nbsp;<a href="https://github.com/tsoding/olive.c/blob/master/demos/triangle3d.c">demos/triangle3d.c</a></p>
     <canvas id="app-triangle3d"></canvas>
 
     <script src="js/vc.js"></script>