We don't have anything specifically to do that, but it would be pretty easy to add manually with simple javascript.
Just add the text and make it not displayed on the page:
<div id="afterSubmit" style="display:none;"> Thank you for submitting the form </div>
Then add code to the onsubmit event of the form to display it:
<form onsubmit="document.getElementById('afterSubmit').style.display = 'block';">