Update docs/configuring-playbook-conduit.md: add the common section "Extending the configuration"

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

docs/configuring-playbook-conduit.md

@@ -16,6 +16,15 @@ To use Conduit, you **generally** need to add the following configuration to you
 matrix_homeserver_implementation: conduit
 ```
 
+### Extending the configuration
+
+There are some additional things you may wish to configure about the server.
+
+Take a look at:
+
+- `roles/custom/matrix-conduit/defaults/main.yml` for some variables that you can customize via your `vars.yml` file
+- `roles/custom/matrix-conduit/templates/conduit.toml.j2` for the server's default configuration
+
 ## Creating the first user account
 
 Since it is difficult to create the first user account on Conduit (see [famedly/conduit#276](https://gitlab.com/famedly/conduit/-/issues/276) and [famedly/conduit#354](https://gitlab.com/famedly/conduit/-/merge_requests/354)) and it does not support [registering users](registering-users.md) (via the command line or via the playbook) like Synapse and Dendrite do, we recommend the following procedure: