diff --git a/doc/README.md b/doc/README.md
index ad34135..ff79269 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -312,6 +312,9 @@ grade_rate_id appears to be consistently 800 iff maiden race and 900 iff debut r
 recommend_class_id appears to be consistently 1 iff maiden race or debut race, 2 iff pre-op, 3 iff op; but other values are confusing.
 so, it doesn't seem like there's a particular flag that identifies maiden races, despite the restrictions on when they appear in the ui.
 
+race_course_set defines the racecourse, e.g. hanshin 1600 turf, that a given race occurs on.
+notably, stat thresholds are defined here via join to race_course_set_status, rather than in course event data.
+
 # trainee definitions
 
 - card_data has universal trainee stats: base skill set, stat growth bonuses ("talent"), default running style