Add documentation for HelperTrait for IDE auto-completion

docs/book/flash-messenger-view-helper.md

@@ -144,3 +144,27 @@ data-dismiss="alert" aria-hidden="true">&times;</button><ul><li>',
     ],
 ],
 ```
+
+## IDE auto-completion in templates
+
+The `Zend\Mvc\Plugin\FlashMessenger\View\HelperTrait` trait can be used to
+provide auto-completion for modern IDEs. It defines the aliases of the view
+helpers in a DocBlock as `@method` tags.
+
+### Usage
+
+In order to allow auto-completion in templates, `$this` variable should be
+type-hinted via a DocBlock at the top of your template. It is recommended that
+you always add the `Zend\View\Renderer\PhpRenderer` as the first type, so that
+the IDE can auto-suggest the default view helpers from `zend-view`. Next, chain
+the `HelperTrait` from `zend-i18n` with a pipe symbol (a.k.a. vertical bar) `|`:
+
+```php
+/**
+ * @var Zend\View\Renderer\PhpRenderer|Zend\Mvc\Plugin\FlashMessenger\View\HelperTrait $this
+ */
+```
+
+You may chain as many `HelperTrait` traits as you like, depending on view
+helpers from which Zend Framework component you are using and would like to
+provide auto-completion for.