Modal Dialog Example: Fix links to modal dialog pattern

For issue #321,  fixed the following:
* The link in the description had incorrect ID in the href.
* Link in the footer was missing href and link text.

examples/dialog-modal/dialog.html

@@ -28,7 +28,7 @@ <h1>Modal Dialog Example</h1>
       </p>
       <p>
         Following is an example implementation of the
-        <a href="../../#dialog">design pattern for modal dialogs.</a>
+        <a href="../../#dialog_modal">design pattern for modal dialogs.</a>
           The below <q>Add Delivery Address</q> button opens a modal dialog that contains two buttons that open other dialogs.
           The accessibility features section explains the rationale for initial focus placement and use of <code>aria-describedby</code> in each dialog.
         </p>
@@ -196,7 +196,7 @@ <h2 id="sc1_label">HTML Source Code</h2>
       </section>
     </main>
     <nav>
-      <a href="../../#pattern_ID">EXAMPLE_NAME Design Pattern in WAI-ARIA Authoring Practices 1.1</a>
+      <a href="../../#dialog_modal">Modal Dialog Design Pattern in WAI-ARIA Authoring Practices 1.1</a>
     </nav>
   </div>
   <div id="dialog_layer">