Indicate that responsibility for system updates is out-of-scope for this playbook

docs/installing.md

@@ -157,6 +157,8 @@ The upstream projects, which this playbook makes use of, occasionally if not oft
 
 Since it is unsafe to keep outdated services running on the server connected to the internet, please consider to update the playbook and re-run it periodically, in order to keep the services up-to-date.
 
+Also, do not forget to update your system regularly. While this playbook may install basic services, such as Docker, it will not interfere further with system maintenance. Keeping the system itself up-to-date is out of scope for this playbook.
+
 For more information about upgrading or maintaining services with the playbook, take a look at this page: [Upgrading the Matrix services](maintenance-upgrading-services.md)
 
 Feel free to **re-run the setup command any time** you think something is wrong with the server configuration. Ansible will take your configuration and update your server to match.