docs: nit for coursegraph README file
docs: nit for coursegraph README file

arbrandes/edx-platform,eduNEXT/edx-platform,eduNEXT/edx-platform,arbrandes/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,angelapper/edx-platform