docs: Adding readme for auth_exchange app (#27803)
docs: Adding readme for auth_exchange app (#27803)

* docs: Adding readme for auth_exchange app

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