Add previous request command to the docs page.

Author: arusahni

docs/index.html

@@ -98,7 +98,8 @@ <h2 class="subtitle is-uppercase">Other features</h2>
             <ul>
                 <li>Viewing open requests with <code>git req --list</code></li>
                 <li>Targeting different remotes with <code>git req -u</code></li>
-                <li>Generating shell completions <code>git req --completions</code></li>
+                <li>Jumping to your previously-checked out request with <code>git req -</code></li>
+                <li>Generating shell completions with <code>git req --completions</code></li>
             </ul>
             <h2 class="subtitle is-uppercase">Questions? Issues?</h2>
             <p>If you have questions, ask on GitHub, or on <a href="https://twitter.com/IAmAru">Twitter</a>. Please file issues on the <a href="https://github.com/arusahni/git-req/issues">GitHub project</a>.</p>