docs: update content-begin hook

exampleSite/layouts/partials/hooks/content-begin.html

@@ -1,5 +1,9 @@
 <div class="alert alert-success" role="alert">
-    Our <a href="https://github.com/hbstack/theme" class="alert-link text-decoration-underline">new theme</a> is available now, please consider giving it a try for your new static sites. :)
+  🎉 Our
+  <a href="https://github.com/hbstack/theme-cards" class="alert-link text-decoration-underline" target="_blank">
+    new modular theme
+  </a>
+  is available now, which ships with much more features and higher flexibility, please consider giving it a try for your new static sites. :)
 </div>
 
 {{- if eq .Type "docs" -}}