Describe '-p' as a short form of '--patch' in synopsis. Also include a better
explanation of this option and additionally refer the reader to the patch mode
description of git-add documentation.
Helped-by: Jeff King <peff@peff.net> Mentored-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Valentin Haenel <valentin.haenel@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>