Add rodauth-openapi to the website

www/pages/documentation.erb

@@ -107,9 +107,10 @@
   <li><a href="https://gitlab.com/honeyryderchuck/rodauth-select-account">rodauth-select-account</a>: Support logging into multiple accounts in the same session.</li>
 </ul>
 
-<h2 id="external-guides">External Guides</h2>
+<h2 id="external-documentation">External Documentation</h2>
 
 <ul>
+  <li><a href="https://github.com/janko/rodauth-openapi">rodauth-openapi</a>: Generate OpenAPI documentation for your Rodauth endpoints</li>
   <li><a href="https://documenter.getpostman.com/view/26686011/2s9YC7SWn9">Documentation of Rodauth routes for JSON requests</a></li>
 </ul>