Update middle.mkd w.r.t. discussion at OpenPGP mailing list on privacy...
Update middle.mkd w.r.t. discussion at OpenPGP mailing list on privacy implications of Version Armor Header. (cf. https://mailarchive.ietf.org/arch/msg/openpgp/WynQyL-9vfVFLe2Jau3jxpT83g8)