✨ Customer-facing docs for GitLab Detective: v0

I'm using this issue to track the work I'm doing to assemble customer-facing docs for GitLab Detective. While working on !55 (merged), I realized it would make sense to focus on the customer-perspective.

• Good docs will help customers use GitLab Detective
• The docs give us a place to record information about how GitLab Detective works and should be used
  • 🛡️ We'll handle some of the recommendations from gitlab-com/support/toolbox/experimental/gitlab-detective-spot#30 in the docs

🐾 Next Steps

• Open a draft MR with the Markdown for the docs I've started
  • !67 (merged)
• Get all applicable security recommendations into the docs
  • Use an account dedicated for use with this tool
  • sudo is required; here's why
  • this is the data we collect
  • this is where data is stored
  • SSH key handling
  • read the playbook to understand the commands
  • notes on how to review the results and transfer them to us
• 🔬 Seek review
  • From Jessie as she works on #82 (closed)
  • Ask on Slack (helpful before driving #27 further)
  • 🏢 🕰️ Chat w/ Tony Marsh

🕰️ Timeline

The first round of this is required to get this to customers. (GitLab Pages is not necessarily in scope for before then.)