Documentation/bisect: improve on (bad|new) and (good|bad)

Documentation/bisect: improve on (bad|new) and (good|bad)

The following part of the description:

git bisect (bad|new) [<rev>]
git bisect (good|old) [<rev>...]

may be a bit confusing, as a reader may wonder if instead it should be:

git bisect (bad|good) [<rev>]
git bisect (old|new) [<rev>...]

Of course the difference between "[<rev>]" and "[<rev>...]" should hint
that there is a good reason for the way it is.

But we can further clarify and complete the description by adding
"<term-new>" and "<term-old>" to the "bad|new" and "good|old"
alternatives.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>