add warning

booking.admin.inc

@@ -30,7 +30,7 @@ function booking_admin() {
   $form['email']['booking_enable_html_mail'] = array(
     '#type' => 'radios',
     '#title' => t('Enable html emails?'),
-    '#description' => t('Turn this feature on for html based emails, otherwise plaintext emails will be used. HTML based emails will require a custom template file to be defined.'),
+    '#description' => t('Turn this feature on for html based emails, otherwise plaintext emails will be used. HTML based emails will require a custom template file to be defined.<br /><strong>WARNING: This will reset all existing mail definitions.</strong> Take care before changing this value.'),
     '#options' => array(
       0 => t('No'),
       t('Yes')