Add first-day-of-week admin area config note

doc/user/admin_area/settings/index.md

@@ -14,6 +14,10 @@ include:
 - [Usage statistics](usage_statistics.md)
 - [Visibility and access controls](visibility_and_access_controls.md)
 
+NOTE: **Note:**
+You can change the [first day of the week](../../profile/preferences.md) for the entire GitLab instance
+in the **Localization** section of **Admin area > Settings > Preferences**.
+
 ## GitLab.com admin area settings
 
 Most of the settings under the admin area change the behavior of the whole