docs: improve forms usage with examples

docs/components/content/examples/SelectExample.vue

@@ -0,0 +1,9 @@
+<script setup>
+const countries = ['United States', 'Canada', 'Mexico']
+
+const country = ref(countries[0])
+</script>
+
+<template>
+  <USelect v-model="country" :options="countries" />
+</template>