docs: improve forms usage with examples

docs/content/3.forms/2.textarea.md

@@ -5,11 +5,22 @@ description: Display a textarea field.
 
 ## Usage
 
-::component-card
----
-baseProps:
-  name: 'textarea'
----
+Use a `v-model` to make the Textarea reactive.
+
+::component-example
+#default
+:textarea-example
+
+#code
+```vue
+<script setup>
+const value = ref('')
+</script>
+
+<template>
+  <UTextarea v-model="value" />
+</template>
+```
 ::
 
 ### Style