git-worktree.txt: keep subcommand listing in alphabetical order

git-worktree.txt: keep subcommand listing in alphabetical order

This is probably not the best order. But it makes it no-brainer to know
where to insert new commands. At some point we might want to reorder at
least the synopsis part again, grouping commonly use subcommands together.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>