Add paragraph to broadcast settings form

The form is going to change to remove all existing permissions when it
is submitted, so this adds a paragraph to explain that.

app/templates/views/service-settings/service-confirm-broadcast-account-type.html

@@ -41,6 +41,10 @@
         </p>
       {% endif %}
 
+      <p class="govuk-body">
+        All team member permissions will be removed.
+      </p>
+
       {% call form_wrapper() %}
         {{ page_footer('Confirm') }}
       {% endcall %}