Update docs/configuring-playbook-traefik.md: add the common section "Installing"

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

docs/configuring-playbook-traefik.md

@@ -173,6 +173,19 @@ traefik_configuration_extension_yaml: |
 
 See the dedicated [Adjusting SSL certificate retrieval](configuring-playbook-ssl-certificates.md) documentation page.
 
+## Installing
+
+After configuring the playbook, run it with [playbook tags](playbook-tags.md) as below:
+
+<!-- NOTE: let this conservative command run (instead of install-all) to make it clear that failure of the command means something is clearly broken. -->
+```sh
+ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,start
+```
+
+The shortcut commands with the [`just` program](just.md) are also available: `just install-all` or `just setup-all`
+
+`just install-all` is useful for maintaining your setup quickly ([2x-5x faster](../CHANGELOG.md#2x-5x-performance-improvements-in-playbook-runtime) than `just setup-all`) when its components remain unchanged. If you adjust your `vars.yml` to remove other components, you'd need to run `just setup-all`, or these components will still remain installed. Note these shortcuts run the `ensure-matrix-users-created` tag too.
+
 ## Troubleshooting
 
 As with all other services, you can find the logs in [systemd-journald](https://www.freedesktop.org/software/systemd/man/systemd-journald.service.html) by logging in to the server with SSH and running `journalctl -fu matrix-traefik`.