docs: more docs

docs/main-concepts/04-hooks.md

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+```rust
+fn Example(cx: &mut Context<()>) -> VNode {
+    let service = use_combubulator(cx);
+    let Status { name, pending, count } = service.info();
+    html! {
+        <div>
+            <p> "Hello, {name}!" </p>
+            <p> "Status: {pending}!" </p>
+            <p> "Count {count}!" </p>
+            <button onclick=|_| service.update()>
+                "Refresh services"
+            </button>
+        </div>
+    }
+}
+```