Add documentation to Data.Value (#6220)

Author: ana-pantilie

plutus-ledger-api/src/PlutusLedgerApi/V1/Data/Value.hs

@@ -1,3 +1,7 @@
+-- TODO: this module adds a copy of the 'Value' type
+-- in which the underlying maps are 'Data.AssocMap'.
+-- !!WARNING!!: this is currently experimental so do not use in production code!
+
 -- editorconfig-checker-disable-file
 {-# LANGUAGE DeriveAnyClass     #-}
 {-# LANGUAGE DeriveDataTypeable #-}