add a desktop eval example

examples/eval.rs

@@ -0,0 +1,25 @@
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::desktop::launch(app);
+}
+
+fn app(cx: Scope) -> Element {
+    let script = use_state(&cx, String::new);
+    let eval = use_eval(&cx);
+
+    cx.render(rsx! {
+        div {
+            input {
+                placeholder: "Enter an expression",
+                value: "{script}",
+                oninput: move |e| script.set(e.value.clone()),
+            }
+            button {
+                onclick: move |_| eval(script),
+
+                "Execute"
+            }
+        }
+    })
+}