chore: bootstrap module from working instance and add install guide

events/DonationSettlementEvent.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace humhub\modules\donations\events;
+
+use humhub\modules\donations\models\DonationGoal;
+use humhub\modules\donations\models\DonationTransaction;
+use yii\base\Event;
+
+class DonationSettlementEvent extends Event
+{
+    public DonationTransaction $transaction;
+    public ?DonationGoal $goal = null;
+    public array $payload = [];
+}