Update docs/configuring-playbook-email.md: copy the common section for installing

The copyright header covers this one.

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

docs/configuring-playbook-email.md

@@ -47,6 +47,19 @@ Note that disabling exim-relay will stop email-notifications and other similar f
 
 See [this entry on the FAQ](faq.md#how-do-i-optimize-this-setup-for-a-low-power-server) for other possible optimizations for a low-power server.
 
+## 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
 
 See [this section](https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay/blob/main/docs/configuring-exim-relay.md#troubleshooting) on the role's documentation for details.