docs(dialog): explain how to show multiple dialogs

src/components/dialog/dialog.js

@@ -200,6 +200,25 @@ function MdDialogDirective($$rAF, $mdTheming, $mdDialog) {
  * })(angular);
  * </hljs>
  *
+ * ### Multiple Dialogs
+ * Using the `multiple` option for the `$mdDialog` service allows developers to show multiple dialogs
+ * at the same time.
+ *
+ * <hljs lang="js">
+ *   // From plain options
+ *   $mdDialog.show({
+ *     multiple: true
+ *   });
+ *
+ *   // From a dialog preset
+ *   $mdDialog.show(
+ *     $mdDialog
+ *       .alert()
+ *       .multiple(true)
+ *   );
+ *
+ * </hljs>
+ *
  * ### Pre-Rendered Dialogs
  * By using the `contentElement` option, it is possible to use an already existing element in the DOM.
  *
@@ -565,7 +584,7 @@ function MdDialogProvider($$interimElementProvider) {
   return $$interimElementProvider('$mdDialog')
     .setDefaults({
       methods: ['disableParentScroll', 'hasBackdrop', 'clickOutsideToClose', 'escapeToClose',
-          'targetEvent', 'closeTo', 'openFrom', 'parent', 'fullscreen'],
+          'targetEvent', 'closeTo', 'openFrom', 'parent', 'fullscreen', 'multiple'],
       options: dialogDefaultOptions
     })
     .addPreset('alert', {