mod_cloud_notify_extensions: Add note about dependency
Noting here because people might not click through to see it on the
mod_cloud_notify_encrypted page.
<tr>
<td colspan="2">
<script src="https://hcaptcha.com/1/api.js" async defer></script>
<div class="h-captcha" data-sitekey="{captcha_public_key}"></div>
</td>
</tr>