docs(guide/directive): update directive restrict options

- add missing 'C' restriction for class names

docs/content/guide/directive.ngdoc

@@ -284,14 +284,18 @@ If we simply put a `<my-customer>` element into the HTML, it doesn't work.
 
 <div class="alert alert-waring">
 **Note:** When you create a directive, it is restricted to attribute only by default. In order to
-create directives that are triggered by element name, you need to use the `restrict` option.
+create directives that are triggered by element or class name, you need to use the `restrict` option.
 </div>
 
 The `restrict` option is typically set to:
 
 * `'A'` - only matches attribute name
 * `'E'` - only matches element name
-* `'AE'` - matches either attribute or element name
+* `'C'` - only matches class name
+
+These restictions can all be combined as needed:
+
+* `'AEC'` - matches either attribure or element or class name
 
 Let's change our directive to use `restrict: 'E'`: