docs/manual: add useful tips on patch versioning and patch submission

Added an alternative on patch versioning (the -v option) and added a
tip on how to automatically mark a previous commit as superseded.

[Thomas: minor tweaks.]

Signed-off-by: Francesco Nwokeka <francesco.nwokeka@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>