Use the `help-text` attribute to add a descriptive “help text”.
For help texts that contain HTML, use the `help-text` slot instead.

```html
<div class="flex gap-12">
  <sd-radio-group orientation="vertical" value="1" help-text="Help text attribute" label="Group label" required>
    <sd-radio value="1">Radio 1</sd-radio>
    <sd-radio value="2">Radio 2</sd-radio>
    <sd-radio value="3">Radio 3</sd-radio>
  </sd-radio-group>
</div>
```