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.
Introduction
============
This module attempts to sanitize XHTML-IM messages.
It does **not** attempt to sanitize any CSS embedded in `style`
attributes, these are instead stripped by default.
Configuration
=============
Option Type Default
------------------------ --------- ---------
`strip_xhtml_style` boolean `true`
`bounce_invalid_xhtml` boolean `false`