Add publication to testimonials.rst
Add publication to testimonials.rst

Thanks for the excellent tool.  arXiv:1202.3665 is reference number 40 within the added paper.
willvousden/emcee,pkgw/emcee,drphilmarshall/emcee,linan7788626/emcee,ipashchenko/emcee,farr/emcee,ga7g08/emcee,joezuntz/emcee,elkingtonmcb/emcee,dfm/emcee,johnbachman/emcee,willvousden/emcee,jellis18/emcee3,johnbachman/emcee,dfm/emcee,dfm/emcee3