add example of markdown slide and element attributes

plugin/markdown/example.html

@@ -68,20 +68,35 @@
                     </script>
                 </section>
 
+                <!-- Slide attributes -->
+                <section data-markdown>
+                    <script type="text/template">
+                        <!-- .slide: data-background="#000000" -->
+                        ## Slide attributes
+                    </script>
+                </section>
+
+                <!-- Element attributes -->
+                <section data-markdown>
+                    <script type="text/template">
+                        ## Element attributes
+                        - Item 1 <!-- .element: class="fragment" data-fragment-index="2" -->
+                        - Item 2 <!-- .element: class="fragment" data-fragment-index="1" -->
+                    </script>
+                </section>
+
                 <!-- Code -->
-                <section>
-                    <section data-markdown>
-                        <script type="text/template">
-                            ```php
-                            public function foo()
-                            {
-                                $foo = array(
-                                    'bar' => 'bar'
-                                )
-                            }
-                            ```
-                        </script>
-                    </section>
+                <section data-markdown>
+                    <script type="text/template">
+                        ```php
+                        public function foo()
+                        {
+                            $foo = array(
+                                'bar' => 'bar'
+                            )
+                        }
+                        ```
+                    </script>
                 </section>
 
             </div>