Remove cloudformation references from Readme.
Remove cloudformation references from Readme.

Edx no longer uses cloudformation, and the templates haven't been in our repos since 2015.
stvstnfrd/configuration,EDUlib/configuration,edx/configuration,stvstnfrd/configuration,arbrandes/edx-configuration,arbrandes/edx-configuration,appsembler/configuration,edx/configuration,mitodl/configuration,edx/configuration,arbrandes/edx-configuration,arbrandes/edx-configuration,mitodl/configuration,stvstnfrd/configuration,mitodl/configuration,appsembler/configuration,EDUlib/configuration,EDUlib/configuration,stvstnfrd/configuration,stvstnfrd/configuration,arbrandes/edx-configuration,mitodl/configuration,appsembler/configuration,EDUlib/configuration,edx/configuration,EDUlib/configuration,appsembler/configuration