One of git-worktree's roles is to populate the new worktree, much like
git-checkout, and thus, for convenience, ought to support several of the
same shortcuts. Toward this goal, add a --detach option to detach HEAD
in the new worktree.
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>