Update -ac_sapling details

[smk762]

From KomodoPlatform/komodo#613

Consider adding to the documentation a note that new AC chains must include the -ac_sapling=1 parameter to support private transactions from the beginning. Otherwise, these chains will not be able to send shielded transactions until sapling activation, as old Sprout proofs are no longer supported and additionally, all Sprout transactions have been prohibited since February 15, 2019 by consensus rules.