docs(guide/directive): explain how to require multiple controllers

Closes angular#8524

Author: James Kleeh

docs/content/guide/directive.ngdoc

@@ -909,6 +909,30 @@ Looking back at `myPane`'s definition, notice the last argument in its `link` fu
 When a directive requires a controller, it receives that controller as the fourth argument of its
 `link` function. Taking advantage of this, `myPane` can call the `addPane` function of `myTabs`.
 
+If multiple controllers are required, the `require` option of the directive can take an array argument.
+The corresponding parameter being sent to the `link` function will also be an array.
+
+```js
+angular.module('docsTabsExample', [])
+  .directive('myPane', function() {
+    return {
+      require: ['^myTabs', '^ngModel'],
+      restrict: 'E',
+      transclude: true,
+      scope: {
+        title: '@'
+      },
+      link: function(scope, element, attrs, controllers) {
+        var tabsCtrl = controllers[0],
+            modelCtrl = controllers[1];
+
+        tabsCtrl.addPane(scope);
+      },
+      templateUrl: 'my-pane.html'
+    };
+  });
+```
+
 Savvy readers may be wondering what the difference is between `link` and `controller`.
 The basic difference is that `controller` can expose an API, and `link` functions can interact with
 controllers using `require`.