feat(about): add revoke authorization instructions

Part of #4

src/app/about/about.component.html

@@ -20,6 +20,7 @@ <h2>YNAB OAuth</h2>
       </ul>
 
       <p>When we authorize with YNAB, we only ever read information. We do not add or edit any transactions to your account. (The YNAB API does not yet offer a read-only mode, otherwise we would use that.)</p>
+      <p>To revoke authorization at any time, visit <a href="https://app.youneedabudget.com/settings">https://app.youneedabudget.com/settings</a>, scroll to "Authorized Applications", and click "Revoke" for Beyond Rule 4. Thanks for trying it out!</p>
     </div>
   </div>
   <div class="row">