Add a Using Bangs section.

source/options/components/page-main.ts

@@ -283,6 +283,20 @@ export class PageMain extends Component<Props, State> {
               button.
             </li>
           </ul>
+
+          <p>Using Bangs:</p>
+          <ul>
+            <li>
+              Once you have a Bang with a valid Search Link, the "Test" button
+              will be enabled. Clicking on that will take you to your Search
+              Link with "test" as the search query.
+            </li>
+            <li>On the DuckDuckGo website, use your custom Bangs directly.</li>
+            <li>
+              With DuckDuckGo set as your browser's default search engine, use
+              your custom Bangs in the address bar.
+            </li>
+          </ul>
         </details>
       </main>
     `;