SubmittingPatches: guidance for multi-series efforts

SubmittingPatches: guidance for multi-series efforts

Occasionally there are efforts to contribute to the Git project that
span more than one patch series in order to achieve a broader goal. By
convention, the maintainer has typically suffixed the topic names with
"-part-one", or "-part-1" and so on.

Document that convention and suggest some guidance on how to structure
proposed topic names for multi-series efforts.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>