docs(guide/Directives): improve description of linking function

The `controller` and `transclude` parameters of the linking function were not
mentioned in the description, but used in the examples.
This commit improves the description and links to the `$compile` API docs
for more details.

Closes #13028

Author: hahla

docs/content/guide/directive.ngdoc

@@ -587,14 +587,24 @@ want to reuse throughout your app.
 In this example we will build a directive that displays the current time.
 Once a second, it updates the DOM to reflect the current time.
 
-Directives that want to modify the DOM typically use the `link` option.
-`link` takes a function with the following signature, `function link(scope, element, attrs) { ... }`
-where:
+Directives that want to modify the DOM typically use the `link` option to register DOM listeners
+as well as update the DOM. It is executed after the template has been cloned and is where
+directive logic will be put.
+
+ `link` takes a function with the following signature,
+`function link(scope, element, attrs, controller, transcludeFn) { ... }`, where:
 
 * `scope` is an Angular scope object.
 * `element` is the jqLite-wrapped element that this directive matches.
 * `attrs` is a hash object with key-value pairs of normalized attribute names and their
   corresponding attribute values.
+* `controller` is the directive's required controller instance(s) or it's own controller (if any).
+  The exact value depends on the directive's require property.
+* `transcludeFn` is a transclude linking function pre-bound to the correct transclusion scope.
+
+<div class="alert alert-info">
+For more details on the `link` option refer to the {@link ng.$compile#-link- `$compile` API} page.
+</div>
 
 In our `link` function, we want to update the displayed time once a second, or whenever a user
 changes the time formatting string that our directive binds to. We will use the `$interval` service