fix(Help): Reflect that the sidebar was reinstated on Opera (#483)

src/static/help.html

@@ -36,7 +36,7 @@ <h2>Features</h2>
 					<li>Quickly check how many landmark regions the page has, via the toolbar icon.</li>
 					<li>Explore landmarks via keyboard shortcuts.</li>
 					<li>Explore landmarks via the toolbar pop-up.</li>
-					<li>Explore landmarks via the browser sidebar (Firefox only&mdash;there is currently a known bug with Opera that prevents the sidebar from being recognised).</li>
+					<li>Explore landmarks via the browser sidebar (Firefox and Opera only).</li>
 					<li>Use the developer tools panel to inspect the code behind landmark regions.</li>
 				</ul>
 				<p>You can change the following <a href="options.html">preferences</a>.</p>