codereview: mention rebase-work in usage message

Include the 'rebase-work' subcommand in the usage message.

Change-Id: I38e5398e89a019669bafeb43429e0bc34988580a
Reviewed-on: https://go-review.googlesource.com/44862
Reviewed-by: Austin Clements <austin@google.com>
1 file changed