Update signature of startPrivateConversation in readme
Update signature of startPrivateConversation in readme

healthchatnow/hcn,EliKrumholz/botkit,tmtkg/botkit,DJ1K1/botkit,stopsatgreen/botkit-slack,gabrielfirmacion/frontdoor-demo,samuelsan/YelpBot,stopsatgreen/botkit-messenger,grindcore819/slackathonMTL,twhit027/lewd-bot,howdyai/botkit,adam-nnl/omgwtfbbq-bot,dcortes22/picnic,DJ1K1/botkit,howdyai/botkit,acrollet/botkit,dhulser/slack-reporting-bot,cbuehnerkemper/botkit-copy,ouadie-lahdioui/botkit,myochum/Triviabot,howdyai/botkit,howdyai/botkit