added another reference

Author: terrancedejesus

rules/integrations/aws/execution_ssm_command_document_created_by_rare_user.toml

@@ -22,7 +22,8 @@ language = "kuery"
 license = "Elastic License v2"
 name = "AWS SSM Command Document Created by Rare User"
 references = [
-    "https://docs.aws.amazon.com/systems-manager/latest/APIReference/API_CreateDocument.html"
+    "https://docs.aws.amazon.com/systems-manager/latest/APIReference/API_CreateDocument.html",
+    "https://docs.aws.amazon.com/systems-manager/latest/userguide/documents.html"
 ]
 risk_score = 21
 rule_id = "50a2bdea-9876-11ef-89db-f661ea17fbcd"