Any way to remove description text on a 'click in' event?

Can't seem to be able to make this work. Maybe there is a way?

We would like to have the verbiage you see below in the description box, when the form loads and the requester scrolls down the form. Like this :

I know we can add it here (red arrow) but my boss really wants the "Please enter a brief..." text in the description box like you see above. Then when the requester starts typing in the description box to clear it out (blank) so they can enter in the problem description. He doesn't think some of our requesters will click on the blue help button.

When I try to add it in FF rules, there isn't an event for description like the other fields:

$CS.setDescription("Please enter a brief description, as well as Business Problem / Opportunity, Detailed Requirements, User Stories or Use Cases, Desired Outcome / Success Criteria, Expected Benefits. Also, attach any Design mock-ups, screenshots, etc");

$CS.setDescription("");

(no event)

Is there any way to accomplish this?