Menu and Menubar Pattern: Add Labeling Guidance

To resolve issue #462, Added the following bullets to
roles, states, and properties subsection of the menu and menubar pattern in aria-practices.html.

> * If a menubar has a visible label, the element with role menubar has aria-labelledby set to a value that refers to the labeling element. Otherwise, the menubar element has a label provided by aria-label.
> * An element with role menu either has:
>    * aria-labelledby set to a value that refers to the menuitem or button that controls its display.
>    * A label provided by aria-label.

aria-practices.html

@@ -1933,10 +1933,21 @@ <h4>WAI-ARIA Roles, States, and Properties</h4>
           <li>When a menu item is disabled, <a href="#aria-disabled" class="state-reference">aria-disabled</a> is set to <code>true</code>.</li>
           <li>Items in a menu may be divided into groups by placing an element with a role of <a href="#separator" class="role-reference">separator</a> between groups. For example, this technique should be used when a menu contains a set of <a href="#menuitemradio" class="role-reference">menuitemradio</a> items. </li>
           <li>All <a href="#separator" class="role-reference">separators</a> should have <a href="#aria-orientation" class="property-reference">aria-orientation</a> consistent with the separator's orientation. </li>
+          <li>
+            If a menubar has a visible label, the element with role <code>menubar</code> has <a href="#aria-labelledby" class="property-reference">aria-labelledby</a> set to a value that refers to the labeling element.
+            Otherwise, the menubar element has a label provided by <a href="#aria-label" class="property-reference">aria-label</a>.
+          </li>
           <li>
             If a menubar is vertically oriented, it has <a class="property-reference" href="#aria-orientation">aria-orientation</a> set to <code>vertical</code>.
             The default value of <code>aria-orientation</code> for a menubar is <code>horizontal</code>.
           </li>
+          <li>
+            An element with role <code>menu</code> either has:
+            <ul>
+              <li><a href="#aria-labelledby" class="property-reference">aria-labelledby</a> set to a value that refers to the menuitem or button that controls its display.</li>
+              <li>A label provided by <a href="#aria-label" class="property-reference">aria-label</a>.</li>
+            </ul>
+          </li>
           <li>
             If a menu is horizontally oriented, it has <a class="property-reference" href="#aria-orientation">aria-orientation</a> set to <code>horizontal</code>.
             The default value of <code>aria-orientation</code> for a menu is <code>vertical</code>.