Add raytracing image to title slide.

src/slide/s1_title.rs

@@ -41,6 +41,7 @@ impl Slide for Title {
             self.examples = vec![
                 ctx_img!(ui.ctx(), "raymarching0.png"),
                 ctx_img!(ui.ctx(), "raymarching1.png"),
+                ctx_img!(ui.ctx(), "raytracing0.png"),
                 ctx_img!(ui.ctx(), "atom0.png"),
                 ctx_img!(ui.ctx(), "atom1.png"),
                 ctx_img!(ui.ctx(), "atom2.png"),