README: add haproxy docs
README: add haproxy docs

harbur/haproxy-consul,benschumacher/haproxy-consul,jefflaplante/haproxy-consul,jfindley/haproxy-consul,udomsak/haproxy-consul,udacity/haproxy-consul,CiscoCloud/haproxy-consul,jmccarty3/haproxy-consul,cmoad/haproxy-consul