Edit docs/configuring-playbook-bridge-hookshot.md: create the "extending the configuration" section

This follows fea8df5ca2.

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

docs/configuring-playbook-bridge-hookshot.md

@@ -34,7 +34,9 @@ For each of the services (GitHub, GitLab, Jira, Figma, generic webhooks) fill in
 
 Take special note of the `matrix_hookshot_*_enabled` variables. Services that need no further configuration are enabled by default (GitLab, Generic), while you must first add the required configuration and enable the others (GitHub, Jira, Figma).
 
-Other configuration options are available via the `matrix_hookshot_configuration_extension_yaml` and `matrix_hookshot_registration_extension_yaml` variables.
+### Extending the configuration
+
+You can configure additional options by adding 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.