Add return info for run_mcmc
Add return info for run_mcmc

linan7788626/emcee,willvousden/emcee,ipashchenko/emcee,pkgw/emcee,dfm/emcee,ga7g08/emcee,johnbachman/emcee,farr/emcee,willvousden/emcee,johnbachman/emcee,elkingtonmcb/emcee,dfm/emcee,joezuntz/emcee,drphilmarshall/emcee