editorial: improve role index introduction (#2083)

Reduces contradiction between first and second paragraph.

Closes #2082

Author: pkra

index.html

@@ -862,7 +862,7 @@ <h3>Window Roles</h3>
 	</section>
 	<section id="role_definitions">
 		<h2>Definition of Roles</h2>
-		<p>Below is an alphabetical list of <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> <a>roles</a> to be used by authors.</p>
+		<p>Below is an alphabetical list of <abbr title="Accessible Rich Internet Applications">WAI-ARIA</abbr> <a>roles</a>.</p>
 		<p>Abstract roles are used for the ontology. Authors MUST NOT use abstract roles in content.</p>
 		<p id="index_role">Placeholder for compact list of roles</p>
 		<div class="role" id="alert">