Update VBO explanation

src/main.cc

@@ -31,7 +31,7 @@ struct App {
   GLuint        vao;
 
   // The buffer that contains all the vertex data
-  // e.g. assume 3 vertices with position, colour and uv
+  // e.g. assume 3 vertices with position, colour and uv, the buffer would look like this
   //  -----------------------------------------------------------------------------------
   // | position1 | colour1 | uv1 | position2 | colour2 | uv2 | position3 | colour3 | uv3 |
   //  -----------------------------------------------------------------------------------