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

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

docs/configuring-playbook-bridge-hookshot.md

@@ -38,7 +38,12 @@ Take special note of the `matrix_hookshot_*_enabled` variables. Services that ne
 
 ### Extending the configuration
 
-You can configure additional options by adding the `matrix_hookshot_configuration_extension_yaml` and `matrix_hookshot_registration_extension_yaml` variables.
+There are some additional things you may wish to configure about the bridge.
+
+Take a look at:
+
+- `roles/custom/matrix-bridge-hookshot/defaults/main.yml` for some variables that you can customize via your `vars.yml` file
+- `roles/custom/matrix-bridge-hookshot/templates/config.yml.j2` for the bridge's default configuration. You can override settings (even those that don't have dedicated playbook variables) using the `matrix_hookshot_configuration_extension_yaml` and `matrix_hookshot_registration_extension_yaml` variables
 
 Refer the [official instructions](https://matrix-org.github.io/matrix-hookshot/latest/setup.html) and the comments in [main.yml](../roles/custom/matrix-bridge-hookshot/defaults/main.yml) to learn what the individual options do.