Add KB instructions on SE testing environment
Fixes https://gitlab.com/gitlab-com/support/issues/54 - replacing !3098 (closed)
Requires the completion of !3381 (merged)
- Instructions on using VMware + Docker
- Instructions on using Digital Ocean + Docker
- Include installation of Docker + Docker-Machine
- Installation of GitLab custom version
cc// @gl-support
Edited by Cynthia "Arty" Ng