bisect: document command line arguments for "bisect start"

The syntax commonly used for alternatives is --opt-(a|b), not
--opt-{a,b}.

List bad/new and good/old consistently in this order, to be
consistent with the description for "git bisect terms".  Clarify
<term> to either <term-old> or <term-new> to make them consistent
with the description of "git bisect (good|bad)" subcommands.

Suggested-by: Matthieu Moy <git@matthieu-moy.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-bisect.txt

@@ -16,7 +16,7 @@ DESCRIPTION
 The command takes various subcommands, and different options depending
 on the subcommand:
 
- git bisect start [--term-{new,bad}=<term> --term-{old,good}=<term>]
+ git bisect start [--term-(bad|new)=<term-new> --term-(good|old)=<term-old>]
 		  [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<paths>...]
  git bisect (bad|new|<term-new>) [<rev>]
  git bisect (good|old|<term-old>) [<rev>...]