diff --git a/download_land_registry.py b/download_land_registry.py
index 7cfa695..e0a1699 100644
--- a/download_land_registry.py
+++ b/download_land_registry.py
@@ -59,6 +59,7 @@ def convert_to_parquet(csv_path: Path, parquet_path: Path) -> None:
     """Convert CSV to Parquet using Polars."""
     print("Converting to Parquet...")
 
+    # https://www.gov.uk/guidance/about-the-price-paid-data
     # Land Registry CSV columns
     columns = [
         "transaction_id",