Forms are generated using default templates. These can be found in
/packages/acs-templating/resources/forms. When I was dealing with
this question, I would copy the standard form to another name and
then make the changes in the new. You can tell your form to
use this new template in the formtemplate tag by using the style
option:
<formtemplate id="my_form"
style="noblue"></formtemplate>
Whenever I've needed to add a short amount of help text, I would use
the -label option to ::template::element. -label can take any text,
including html.