docs: update readme with secrets manager resource ref

Signed-off-by: Sonu Saha <sonu.saha@progress.com>

README.md

@@ -377,6 +377,7 @@ The following resources are available in the InSpec GCP Profile
 | [google_vertex_ai_training_pipeline](docs/resources/google_vertex_ai_training_pipeline.md)                           | [google_vertex_ai_training_pipelines](docs/resources/google_vertex_ai_training_pipelines.md)             |
 | [google_composer_project_location_environment](docs/resources/google_composer_project_location_environment.md)                           | [google_composer_project_location_environments](docs/resources/google_composer_project_location_environments.md)             |
 | [google_compute_service_attachment](docs/resources/google_compute_service_attachment.md)                           | [google_compute_service_attachments](docs/resources/google_compute_service_attachments.md)             |
+| [google_secret_manager_secret](docs/resources/google_secret_manager_secret.md)                           | [google_secret_manager_secrets](docs/resources/google_secret_manager_secrets.md)             |
 
 ## Examples