Fix graphic in GitLab Geo documentation
Came up during demo, the graphic (https://docs.gitlab.com/ee/gitlab-geo/img/geo-overview.png) on https://docs.gitlab.com/ee/gitlab-geo/#overview needs an update.
- San Francisco Team and Netherlands Team should be San Francisco server and Netherlands server
- Consider calling Mirror "Secondary" instead
- Use new images or move images to be correct and current team members.
@luke is this in your wheelhouse?