styleguide: Add WIP message

styleguide/generator/index.html

@@ -35,8 +35,17 @@
                         data-icon="light" class="glow"></i></a></li>
             </ul>
         </nav>
-        <main class="generator">
-            <div>
+        <main>
+            <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>
+            <div class="generator">
 
                 <div>
                     <input id="file_input" type="file" name="image" accept="image/*">