docs(marketing): add parameter placeholder to /plannotator-annotate command

For provenance purposes, this commit was AI assisted.

Author: backnotprop

apps/marketing/src/pages/index.astro

@@ -315,7 +315,7 @@ import AnnoReplace from '../components/landing/AnnoReplace.astro';
               <span class="cap-desc">Automatic: hooks into your agent's plan step</span>
             </div>
             <div class="cap-item">
-              <code class="cap-cmd">/plannotator-annotate</code>
+              <code class="cap-cmd">/plannotator-annotate &lt;file|folder|url&gt;</code>
               <span class="cap-desc">Annotate any markdown, html, folder, or URL and send feedback</span>
             </div>
             <div class="cap-item">