Document API to configure ACP menu items via bootstrap script

docs/migration/wsc60/php.md

@@ -32,3 +32,7 @@ class MyForm extends AbstractForm {
 ## RSS Feeds
 
 A [new API](../../php/api/rss_feeds.md) for the output of content as an RSS feed has been introduced. 
+
+## ACP Menu Items
+
+A [new API](../../package/acp-menu-items.md) for adding ACP menu items has been introduced. The previous option of adding menu entries via PIP is still supported, but is to be discontinued in the long term.

docs/package/acp-menu-items.md

@@ -0,0 +1,47 @@
+# ACP Menu Items
+
+The API for the ACP menu items allows you to add your own menu items in the admin panel for your package.
+
+Since WoltLab Suite 6.1 you can attach an event listener to the `wcf\system\menu\acp\event\AcpMenuCollecting` event inside a bootstrap script to lazily register your ACP menu items.
+
+The `register` method of the event expects an object of the type `wcf\system\menu\acp\AcpMenuItem` as a parameter. An `AcpMenuItem` object consists of the following parameters:
+
+| Name | Type | Description |
+|------|------|-------------|
+| `$menuItem` | string | Identifier of the item; must be unique |
+| `$title` | string | (Optional) title of the item; if omitted `$menuItem` is used as language variable |
+| `$parentMenuItem` | string | (Optional) identifier of the parent item |
+| `$link` | string | (Optional) URL of the linked page |
+| `$icon` | ?FontAwesomeIcon | (Optional) icon of the item |
+
+Example:
+
+```php
+<?php
+
+use wcf\system\event\EventHandler;
+use wcf\system\menu\acp\AcpMenuItem;
+use wcf\system\menu\acp\event\AcpMenuCollecting;
+use wcf\system\request\LinkHandler;
+use wcf\system\style\FontAwesomeIcon;
+
+return static function (): void {
+    EventHandler::getInstance()->register(AcpMenuCollecting::class, static function (AcpMenuCollecting $event) {
+        $event->register(new AcpMenuItem(
+            "com.woltlab.foor.bar",
+            'Example Title',
+            'wcf.acp.menu.link.application'
+        ));
+
+        if ($currentUserHasSomeSpecificPermission) {
+            $event->register(new AcpMenuItem(
+                "com.woltlab.foor.bar.add",
+                'Example Add Title',
+                "com.woltlab.foor.bar",
+                LinkHandler::getInstance()->getControllerLink(FooAddForm::class),
+                FontAwesomeIcon::fromString('plus;false')
+            ));
+        }
+    });
+};
+```

mkdocs.yml

@@ -113,6 +113,7 @@ nav:
           - 'userNotificationEvent': 'package/pip/user-notification-event.md'
           - 'userOption': 'package/pip/user-option.md'
           - 'userProfileMenu': 'package/pip/user-profile-menu.md'
+      - 'ACP Menu Items': 'package/acp-menu-items.md'
       - 'Database PHP API': 'package/database-php-api.md'
 
   - 'Migration':