Link to Racket docs for prefab struct labels

syndicate/mc/preserve.md

@@ -603,6 +603,9 @@ encodes to
         (struct person thing (name date-of-birth) #:prefab)
         (struct titled person (title) #:prefab)
 
+    For more detail on Racket's representations of record labels, see
+    [the Racket documentation for `make-prefab-struct`](http://docs.racket-lang.org/reference/structutils.html#%28def._%28%28quote._~23~25kernel%29._make-prefab-struct%29%29).
+
 ## Conventions for Common Data Types
 
 The `Value` data type is essentially an S-Expression, able to