Add warning on debugger tour section in web

examples/tour.rs

@@ -622,11 +622,19 @@ impl<'a> Step {
                 "Give it a shot! Check the following checkbox to be able to \
                  see element boundaries.",
             ))
-            .push(Checkbox::new(
+            .push(if cfg!(target_arch = "wasm32") {
+                Element::new(
+                    Text::new("Not available on web yet!")
+                        .color([0.7, 0.7, 0.7])
+                        .horizontal_alignment(HorizontalAlignment::Center),
+                )
+            } else {
+                Element::new(Checkbox::new(
                     debug,
                     "Explain layout",
                     StepMessage::DebugToggled,
                 ))
+            })
             .push(Text::new("Feel free to go back and take a look."))
     }