SubmittingPatches: Clarify the Signed-off-by rules

SubmittingPatches: Clarify the Signed-off-by rules

The wording of the Signed-off-by rules could be read as stating that
S-O-B should only be added when the submitter considered the patch
ready for inclusion in git.git.

We also want Signed-off-by to be used for e.g. RFC patches, in case
someone wants to dig an old patch out of the archive and improve
it. Change the wording to recommend a Signed-off-by for all submitted
patches.

The problem with the wording came up in the "[PATCH/RFC] Hacky version
of a glob() driven config include" thread[1]. Bert Wesarg suggested[2]
that it be removed to avoid confusion, which this change implements.

  1. <1273180440-8641-1-git-send-email-avarab@gmail.com>
  2. <AANLkTimziTKL13VKIOcaS1TX1F_xvTVjH8Q398Yx36Us@mail.gmail.com>

Suggested-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>