Document visit-level purchase analysis

README.md

@@ -129,6 +129,19 @@ Combined:
 - `data/review/pipeline_status.json`
 - `data/catalog.csv`
 
+`data/review/purchases.csv` is the main analysis artifact. It is designed to support both:
+- item-level price analysis
+- visit-level analysis such as spend by visit, items per visit, category spend by visit, and retailer/store breakdown
+
+The visit fields are carried directly in `purchases.csv`, so you can pivot on them without extra joins:
+- `order_id`
+- `purchase_date`
+- `retailer`
+- `store_name`
+- `store_number`
+- `store_city`
+- `store_state`
+
 ## Review Workflow
 
 Run `review_products.py` to cleanup unresolved or weakly unified items: