Add a FAQ section to GitPod documentation

Overview

Less advanced users of GitPod + GitLab often have the same questions about how to use GitPod. Often these get posted and answered in our #gitpod channel, but it would be nice to codify these great insights.

Proposal (optional)

• Either a FAQ if a friendly, light-weight approach would be helpful.
• Or, more traditional guidance that just enriches the current docs.