Documentation/process: phrasofix

Devils in the details are found only when the high level design is
refined and gets more detailed, and the appropriate phrase to use to
describe this is "problems are revealed", not "problems are
reviewed".

Reviews may reveal these problems, though ;-)

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>