docs($compile): correct what gets passed to ctrl argument

Closes #11903

Author: Narretz

src/ng/compile.js

@@ -399,13 +399,16 @@
  *   * `controller` - the directive's required controller instance(s) - Instances are shared
  *     among all directives, which allows the directives to use the controllers as a communication
  *     channel. The exact value depends on the directive's `require` property:
+ *       * no controller(s) required: the directive's own controller, or `undefined` if it doesn't have one
  *       * `string`: the controller instance
  *       * `array`: array of controller instances
- *       * no controller(s) required: `undefined`
  *
  *     If a required controller cannot be found, and it is optional, the instance is `null`,
  *     otherwise the {@link error:$compile:ctreq Missing Required Controller} error is thrown.
  *
+ *     Note that you can also require the directive's own controller - it will be made available like
+ *     like any other controller.
+ *
  *   * `transcludeFn` - A transclude linking function pre-bound to the correct transclusion scope.
  *     This is the same as the `$transclude`
  *     parameter of directive controllers, see there for details.