docs: improve forms usage with examples

docs/content/3.forms/5.checkbox.md

@@ -5,11 +5,22 @@ description: Display a checkbox field.
 
 ## Usage
 
-::component-card
----
-baseProps:
-  name: 'checkbox'
----
+Use a `v-model` to make the Checkbox reactive.
+
+::component-example
+#default
+:checkbox-example
+
+#code
+```vue
+<script setup>
+const selected = ref(false)
+</script>
+
+<template>
+  <UCheckbox v-model="selected" name="notifications" label="Notifications" />
+</template>
+```
 ::
 
 ### Label