Add docstring to extract method

parsons/google/google_bigquery.py

@@ -1377,6 +1377,22 @@ def extract(
         project: Optional[str] = None,
         gzip: bool = False,
     ) -> None:
+        """
+        Extracts a BigQuery table to a Google Cloud Storage bucket.
+
+        Args:
+            dataset (str): The BigQuery dataset containing the table.
+            table_name (str): The name of the table to extract.
+            gcs_bucket (str): The GCS bucket where the table will be
+              exported.
+            gcs_blob_name (str): The name of the blob in the GCS
+              bucket.
+            project (Optional[str]): The Google Cloud project ID. If
+              not provided, the default project of the client is used.
+            gzip (bool): If True, the exported file will be compressed
+              using GZIP. Defaults to False.
+        """
+
         dataset_ref = bigquery.DatasetReference(project or self.client.project, dataset)
         table_ref = dataset_ref.table(table_name)
         gs_destination = f"gs://{gcs_bucket}/{gcs_blob_name}"