add contributors section
add contributors section

dorian1453/limbo,ruhee/limbo,rizaon/limbo,mmisiewicz/slask,uilab-github/slask,cmyr/debt-bot,llimllib/limbo,kylemsguy/limbo,shawnsi/limbo,llimllib/limbo,joshshadowfax/slask,signalnine/alanabot,freshbooks/limbo,palachu/sdbot,serverdensity/sdbot,TetraEtc/limbo,sentinelleader/limbo,wmv/slackbot-python,Marclass/limbo,NUKnightLab/slask,TetraEtc/limbo,akatrevorjay/slask,kesre/slask,uilab-github/slask,michaelMinar/limbo,UnILabKAIST/slask,Whirlscape/debt-bot