Clarify patch role permissions (#30128)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

api/v4/source/roles.yaml

@@ -100,7 +100,8 @@
 
         ##### Permissions
 
-        `manage_system` permission is required.
+        Must have `sysconsole_write_user_management_permissions` or `manage_system` permission.
+        When updating the role of a system admin, the `manage_system` permission is mandatory.
 
 
         __Minimum server version__: 4.9