Update docs/configuring-playbook-synapse.md: add the sections "Installing" and "Usage"

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

docs/configuring-playbook-synapse.md

@@ -145,13 +145,28 @@ Take a look at:
 - `roles/custom/matrix-synapse/defaults/main.yml` for some variables that you can customize via your `vars.yml` file
 - `roles/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2` for the server's default configuration. You can override settings (even those that don't have dedicated playbook variables) using the `matrix_synapse_configuration_extension_yaml` variable
 
-## Synapse Admin
+## 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.
+
+## Usage
+
+### Synapse Admin
 
 With [Synapse Admin](configuring-playbook-synapse-admin.md), certain Synapse administration tasks (managing users and rooms, etc.) can be performed via a web user-interace.
 
 The playbook can install and configure Synapse Admin for you. For details about it, see [this page](configuring-playbook-synapse-admin.md).
 
-## Monitoring Synapse Metrics with Prometheus and Grafana
+### Monitoring Synapse Metrics with Prometheus and Grafana
 
 This playbook allows you to enable Synapse metrics, which can provide insight into the performance and activity of Synapse.