R1:e19ad8ab8a55

Warn users about using `bin/accountadmin` for first time setup

Summary: The "easy setup" is sort of an exaggeration since it basically just amounts to getting you logged in correctly, but it will probably be more true in the future.

Test Plan: Ran `bin/accountadmin` with zero and more than zero accounts.

Reviewers: asherkin, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7678