docs($compile): correct transcludeControllers definition

Closes #13793

Author: Narretz

src/ng/compile.js

@@ -708,8 +708,15 @@
  *        directives; if given, it will be passed through to the link functions of
  *        directives found in `element` during compilation.
  *      * `transcludeControllers` - an object hash with keys that map controller names
- *        to controller instances; if given, it will make the controllers
- *        available to directives.
+ *        to a hash with the key `instance`, which maps to the controller instance;
+ *        if given, it will make the controllers available to directives on the compileNode:
+ *        ```
+ *        {
+ *          parent: {
+ *            instance: parentControllerInstance
+ *          }
+ *        }
+ *        ```
  *      * `futureParentElement` - defines the parent to which the `cloneAttachFn` will add
  *        the cloned elements; only needed for transcludes that are allowed to contain non html
  *        elements (e.g. SVG elements). See also the directive.controller property.