Add OFF snapshot date to dataset card

README.md

@@ -23,6 +23,8 @@ OFF-AllergenQA-JP8 is a curated benchmark derived from Open Food Facts (OFF) pro
 
 The released examples are restricted to U.S.-market packaged multi-ingredient foods whose raw `ingredients_text` is in English.
 
+For this draft release, the underlying OFF source data snapshot was acquired on March 17, 2026.
+
 Each record represents a `(product_id, allergen)` pair for one of the Japanese 8 priority allergens (JP8). The "JP8" part refers to the target allergen set, not to the language of the product label:
 
 - egg