add examples for onmounted

examples/scroll_to_top.rs

@@ -0,0 +1,33 @@
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus_desktop::launch(app);
+}
+
+fn app(cx: Scope) -> Element {
+    let header_element = use_ref(cx, || None);
+
+    cx.render(rsx!(
+        div {
+            h1 {
+                onmounted: move |cx| {
+                    header_element.set(Some(cx.inner().clone()));
+                },
+                "Scroll to top example"
+            }
+
+            for i in 0..100 {
+                div { "Item {i}" }
+            }
+
+            button {
+                onclick: move |_| {
+                    if let Some(header) = header_element.read().as_ref() {
+                        header.scroll_to(ScrollBehavior::Smooth);
+                    }
+                },
+                "Scroll to top"
+            }
+        }
+    ))
+}