docs: explain Ferese integration model

site/index.html

@@ -93,7 +93,7 @@
             A menu bar, Control Center, Settings, notifications, and desktop
             widgets, designed to work together.
           </p>
-          <a href="docs/">Explore the handbook →</a>
+          <a href="docs/why-ferese.html">Why integration matters →</a>
         </article>
         <article>
           <h2>Make it yours</h2>