Add enterprise policy update_url info to update doc (#2382)

Author: mkaply

src/content/documentation/manage/updating-your-extension.md

@@ -94,6 +94,12 @@ If your extension is not hosted on AMO, you must specify the location of your up
 }
 ```
 
+::: note
+Once an extension is installed, Firefox continues using the `update_url` from the installed version to check for updates. If that update manifest becomes unavailable or you need to move it, existing installations cannot discover a new `update_url` on their own.
+
+[Enterprise Policies](https://firefox-admin-docs.mozilla.org/reference/policies/extensionsettings/) can override an extension's `update_url`, providing a recovery path by redirecting update checks to a new update manifest so future versions can specify a new `update_url`.
+:::
+
 {% endcapture %}
 {% include modules/one-column.liquid,
     id: "enable-update"