Add description about keeping the playbook and services up-to-date

Also: move descriptions about difference between the playbook tags (setup-all and install-all) and about the just "recipe" from installing.md to maintenance-upgrading-services.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/maintenance-upgrading-services.md

@@ -2,9 +2,19 @@
 
 This playbook not only installs the various Matrix services for you, but can also upgrade them as new versions are made available.
 
+While this playbook helps you to set up Matrix services and maintain them, it will **not** automatically run the maintenance task for you. You will need to update the playbook and re-run it **manually**.
+
+The upstream projects, which this playbook makes use of, occasionally if not often suffer from security vulnerabilities (for example, see [here](https://github.com/element-hq/element-web/security) for known ones on Element Web).
+
+Since it is unsafe to keep outdated services running on the server connected to the internet, please consider to update the playbook and re-run it periodically, in order to keep the services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.
+
+The developers of this playbook strive to maintain the playbook updated, so that you can re-run the playbook to address such vulnerabilities. It is **your responsibility** to keep your server and the services on it up-to-date.
+
 If you want to be notified when new versions of Synapse are released, you should join the Synapse Homeowners room: [#homeowners:matrix.org](https://matrix.to/#/#homeowners:matrix.org).
 
-To upgrade services:
+## Steps to upgrade the Matrix services
+
+To upgrade the services:
 
 - update your playbook directory and all upstream Ansible roles (defined in the `requirements.yml` file) using:
 
@@ -13,6 +23,14 @@ To upgrade services:
 
 - take a look at [the changelog](../CHANGELOG.md) to see if there have been any backward-incompatible changes that you need to take care of
 
-- re-run the [playbook setup](installing.md) and restart all services: `just install-all` or `just setup-all`
+- re-run the [playbook setup](installing.md#maintaining-your-setup-in-the-future) and restart all services:
+
+  ```sh
+  ansible-playbook -i inventory/hosts setup.yml --tags=install-all,start
+  ```
+
+Note that if you remove components from `vars.yml`, or if we switch some component from being installed by default to not being installed by default anymore, you'd need to run the setup command with `--tags=setup-all` instead of `--tags=install-all`. See [this page on the playbook tags](playbook-tags.md) for more information.
+
+A way to invoke these `ansible-playbook` commands with less typing is to use [just](https://github.com/casey/just) to run the "recipe": `just install-all` or `just setup-all`. See [our `justfile`](../justfile) for more information.
 
 **Note**: major version upgrades to the internal PostgreSQL database are not done automatically. To upgrade it, refer to the [upgrading PostgreSQL guide](maintenance-postgres.md#upgrading-postgresql).