Add warning docblock to SendPolicyAnnouncementJob

app/Jobs/SendPolicyAnnouncementJob.php

@@ -6,6 +6,16 @@
 use App\User;
 use Illuminate\Support\Facades\Notification;
 
+/**
+ * WARNING: This job is NOT idempotent. DO NOT RUN IT MULTIPLE TIMES.
+ * There is also no error handling or mechanism for recording which users have been sent an email.
+ *
+ * This has created an issue on production where a user with an empty string as an email address
+ * (due to a request to remove PII) caused Notification::send() to throw an error and the remaining
+ * emails to not be sent.
+ *
+ * DO NOT REPEAT THIS PATTERN FOR OTHER JOBS
+ */
 class SendPolicyAnnouncementJob extends Job {
     public function handle() {
         $users = User::query()->whereNotNull('email')->get();