cherry-pick: prettify the advice message

cherry-pick: prettify the advice message

It's hard to see the "how to commit" part of this message,
which users may want to cut and paste. On top of that,
having it in paragraph form means that a really long commit
name may cause ugly wrapping. Let's make it prettier, like:

  Automatic cherry-pick failed.  After resolving the conflicts,
  mark the corrected paths with 'git add <paths>' or 'git rm <paths>'
  and commit the result with:

          git commit -c HEAD~23

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>