styleguide: Add WIP message

styleguide/index.html

@@ -38,6 +38,16 @@
         <main>
             <h1>Styleguide Easterhegg 2025</h1>
 
+            <div class="alert">
+                <i data-icon="warning"></i>
+                <p>
+                    <strong>Work in progress</strong>
+                    This style guide is still under development.<br>
+                    Not all resources may be available yet, explanations and examples may be missing and things may
+                    change without notice.
+                </p>
+            </div>
+
         </main>
         <script src="assets/script/styleguide.js" type="text/javascript"></script>
     </div>