Fix config flag in README
Fix config flag in README

The readme was using `-c` instead of `-C`, making it a bit confusing to get started.
elbidigital/confd,cvrabie/confd,okushchenko/confd,layerhq/confd,nevermosby/confd,shencan/confd,linearregression/confd,rancher/confd,bacongobbler/confd,gautamk/confd,gautamk/confd,elbidigital/confd,jnummelin/confd,chendh521/confd,Lineberty/confd,glerchundi/renderizr,chendh521/confd,Ropes/confd,bacongobbler/confd,nevermosby/confd,mboersma/confd,Flipkart/confd,aledbf/confd,kelseyhightower/confd,cvrabie/confd,RichardKnop/confd,karthequian/confd,linearregression/confd,kgrvamsi/confd,crunchywelch/confd,blippar/confd,glerchundi/renderizr,alexnauda/confd,say5/confd,glerchundi/confd,jnummelin/confd,agilemobiledev/confd,cloudnautique/confd,zytek/confd,rancher/confd,israelchen/confd,fritzy/confd,Flipkart/confd,zytek/confd,say5/confd,kgrvamsi/confd,PrFalken/confd,beni55/confd,openedbox/confd,karthequian/confd,crandles/confd,kelseyhightower/confd,Flipkart/confd,monder/confd,deis/confd,layerhq/confd,elsonrodriguez/confd,openedbox/confd,beni55/confd,shencan/confd,Fitbit/confd,tomdee/confd,danesparza/confd,RichardKnop/confd,crunchywelch/confd,agilemobiledev/confd,Lineberty/confd,axingblog/confd,deis/confd,aledbf/confd,monder/confd,crandles/confd,okushchenko/confd,blippar/confd,axingblog/confd,elsonrodriguez/confd,Fitbit/confd,tomdee/confd,philipsoutham/confd,Ropes/confd,fritzy/confd,cloudnautique/confd,alexnauda/confd,philipsoutham/confd,danesparza/confd,mboersma/confd,glerchundi/confd,PrFalken/confd,israelchen/confd