docs(SelectMenu): improve async search example

docs/components/content/examples/SelectMenuExampleSearchAsync.vue

@@ -0,0 +1,27 @@
+<script setup>
+const loading = ref(false)
+const selected = ref([])
+
+async function search (q) {
+  loading.value = true
+
+  const users = await $fetch('https://jsonplaceholder.typicode.com/users', { params: { q } })
+
+  loading.value = false
+
+  return users
+}
+</script>
+
+<template>
+  <USelectMenu
+    v-model="selected"
+    :loading="loading"
+    :searchable="search"
+    placeholder="Search for a user..."
+    option-attribute="name"
+    multiple
+    trailing
+    by="id"
+  />
+</template>