Add CONTRIBUTING.md
Add CONTRIBUTING.md

Solves #59

sakimyto/papabot121,DJ1K1/botkit,ouadie-lahdioui/botkit,naokie/botkit,myochum/Triviabot,michaesw/botkit,nhindman/airbnb_bot,howdyai/botkit,twhit027/lewd-bot,dotstudio/slack-bot,cbuehnerkemper/botkit-copy,acrollet/botkit,grindcore819/slackathonMTL,DJ1K1/botkit,gabrielfirmacion/frontdoor-demo,stopsatgreen/botkit-slack,n0bisuke/slack-bot,adam-nnl/omgwtfbbq-bot,healthchatnow/hcn,tmtkg/botkit,howdyai/botkit,ductran96/botkit,amritg/botkit,dhulser/slack-reporting-bot,Catscadia/botkit,pickettd/slack-oregon-trail,vuquangtuan/botkit,dcortes22/picnic,samuelsan/YelpBot,stopsatgreen/botkit-messenger,EliKrumholz/botkit,Philipp-Werminghausen/chuck-norris,howdyai/botkit,howdyai/botkit