Although 1eb07d8 (worktree: add: auto-vivify new branch when
<branch> is omitted, 2015-07-06) updated the documentation when
<branch> became optional, it neglected to update the in-code
usage message. Fix this oversight.
Reported-by: ch3cooli@gmail.com Signed-off-by: Sidhant Sharma <tigerkid001@gmail.com> Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>