implement use_async_memo with reactive context

examples/readme.rs

@@ -1,3 +1,5 @@
+use std::time::Duration;
+
 use dioxus::prelude::*;
 
 fn main() {
@@ -23,7 +25,17 @@ fn app() -> Element {
 fn Child(sig: Signal<i32>) -> Element {
     let doubled = use_memo(move || sig() * 2);
 
+    let tripled = use_async_memo(move || async move {
+        tokio::time::sleep(Duration::from_millis(200)).await;
+        sig() * 3
+    });
+
+    let trippled = use_memo(move || match tripled.value() {
+        Some(v) => v.cloned(),
+        None => 1338,
+    });
+
     rsx! {
-        "The count is: {sig}, doubled: {doubled}"
+        "The count is: {sig}, doubled: {doubled}, tripled: {trippled}"
     }
 }