Replace glob by EventDispatcher

Signed-off-by: Vitor Mattos <vitor@php.rio>

docs/implement-import.md

@@ -1,4 +1,32 @@
 ## Implement import
 
-* Create a new class `lib/Service/Importer/Systems/<ImportName>Service.php` where `<ImportName>` is the name of the source system.
+* Create a new importer class extending `ABoardImportService`
+* Create a listener for event `BoardImportGetAllowedEvent` to enable your importer.
+  > You can read more about listeners on [Nextcloud](https://docs.nextcloud.com/server/latest/developer_manual/basics/events.html?highlight=event#writing-a-listener) doc.
+
+  Example:
+
+```php
+class YourCustomImporterListener {
+    public function handle(Event $event): void {
+        if (!($event instanceof BoardImportGetAllowedEvent)) {
+            return;
+        }
+
+        $event->getService()->addAllowedImportSystem([
+            'name' => YourCustomImporterService::$name,
+            'class' => YourCustomImporterService::class,
+            'internalName' => 'YourCustomImporter'
+        ]);
+    }
+}
+```
+  * Register your listener on your `Application` class like this:
+```php
+$dispatcher = $this->getContainer()->query(IEventDispatcher::class);
+$dispatcher->registerEventListener(
+    BoardImportGetAllowedEvent::class,
+    YourCustomImporterListener::class
+);
+```
 * Use the `lib/Service/Importer/Systems/TrelloJsonService.php` class as inspiration