Add note about retention settings (#1826)

Author: mjankowski

content/en/admin/scaling.md

@@ -478,3 +478,10 @@ These endpoints should both return an HTTP status code of 200, and the text `OK`
 {{< hint style="info" >}}
 You can also use these endpoints for health checks with a third-party monitoring/alerting utility.
 {{< /hint >}}
+
+## User-generated content retention
+
+To prevent runaway growth of stored assets, review the settings under **Administration** > **Content retention** and set them to values appropriate for your server and users. The cleanup task runs via the background job scheduler, and does not need manual triggering or cron settings.
+
+- The media cache retention setting controls how long media from remote users is cached on your server
+- The user archive retention period controls how long backups generated by your own users are kept