Geo - Moving next gen information from doc to handbook
Moving information from the Google Doc (https://docs.google.com/document/d/1azr1CuP6Bm-XB9r4N1LDPjqEIIaesshKMcSdKZBMI1U/edit#heading=h.bt4nkkg49s5h) to the handbook.
Related to: https://gitlab.com/gitlab-org/gitlab-ee/issues/8729
Deployed page for review: https://rnienaber-next-gen-geo.about-src.gitlab.com/handbook/engineering/dev-backend/geo/2019-next-gen-geo.html
Edited by Rachel Nienaber