add selector example to readme

packages/signals/examples/selector.rs

@@ -0,0 +1,30 @@
+#![allow(non_snake_case)]
+
+use dioxus::prelude::*;
+use dioxus_signals::*;
+
+fn main() {
+    dioxus_desktop::launch(app);
+}
+
+fn app(cx: Scope) -> Element {
+    let signal = use_signal(cx, || 0);
+    let doubled = use_selector(cx, move || signal * 2);
+
+    render! {
+        button {
+            onclick: move |_| *signal.write() += 1,
+            "Increase"
+        }
+        Child {
+            signal: doubled
+        }
+    }
+}
+
+#[inline_props]
+fn Child(cx: Scope, signal: ReadOnlySignal<usize>) -> Element {
+    render! {
+        "{signal}"
+    }
+}