bbPress.org

This is one way…

function ntwb_bbp_theme_before_topic_form_notices() {
	?>
	<div class="bbp-template-notice">
		<p>Something here...</p>
		<p>Something else...</p>
	</div>
	<?php

}
add_action( 'bbp_theme_before_topic_form_notices', 'ntwb_bbp_theme_before_topic_form_notices' );

And another is to modify the form-topic.php template.