DOC Add session-manager to changelog

docs/en/04_Changelogs/4.9.0.md

@@ -4,6 +4,7 @@
 
 - [Features and enhancements](#features-and-enhancements)
     - [Image lazy loading](#image-lazy-loading)
+    - [Manage your CMS sessions across devices](#session-manager)
     - [Other new features](#other-features)
 - [Bugfixes](#bugfixes)
 
@@ -40,6 +41,16 @@ SilverStripe\Assets\Image:
 
 CMS authors can disable lazy loading on images added via the WYSIWYG editor in the "Edit image" panel by setting the new "Loading" field to "Eager".
 
+### Manage your CMS sessions across devices {#session-manager}
+
+The [session manager module](https://github.com/silverstripe/silverstripe-session-manager) is a new security focused feature which allows a CMS user to view and manage their active sessions in the CMS within the "My profile" section of the CMS (/admin/myprofile). They can see the device details behind each session and have the ability to revoke these sessions. This new module has been added to `silverstripe/recipe-cms` which is the recommended method of managing Silverstripe CMS dependencies in a project.
+
+Projects that have `silverstripe/recipe-cms` as a requirement in their `composer.json` will automatically get `silverstripe/session-manager` when you run `composer update`. If your project does not use `silverstripe/recipe-cms`, it's recommended that you require `silverstripe/session-manager` in your composer file as a security enhancement. The session manager module requires no configuration and works out-of-the-box.
+
+If your site has the [symbiote/silverstripe-queuedjobs](https://github.com/symbiote/silverstripe-queuedjobs) module installed, then a job will automatically be created that will periodically remove old database records created by the session manager module.
+
+CMS users can review the [Session Manager user help](https://userhelp.silverstripe.org/en/4/managing_your_website/session_manager/) for more information on managing their sessions.
+
 ### Other new features
 
 * [Dot notation support in form fields](https://github.com/silverstripe/silverstripe-framework/pull/9192): Save directly into nested has_one relationships (see [docs](/developer_guides/forms/how_tos/handle_nested_data)).