Clarify team structure

Created by: christinaforney

The homepage of the handbook is essentially a list of the teams we have at Sourcegraph, and this information does not exist anywhere else. This minor hierarchy change helps to clarify this and fill the gap.

I brought the engineering team list up a level to help with this, but understand it's now duplicated (which is sub-optimal). Open to ideas!

Created by: sqs

1. Duplicating the eng team list is fine. Just add Markdown comments in both places mentioning it needs to be updated in both places in sync.
2. I don't like making "teams" the top-level navigation concept. It optimizes for the writer (and specifically the manager of the team), not the reader. It also makes it feel like you can't/shouldn't edit other teams' pages. You could add a note to this page saying that these headers are roughly the teams at Sourcegraph; that would convey the info without having these negative consequences.

Created by: christinaforney

@sqs - does the update I made resolve your concerns? @pecigonzalo - does this change help clarify your request for better understanding the teams at Sourcegraph?