Doc de dév de VigiBoard.

Change-Id: I2bc4a64995cd9bbfd2e6ca9790423f97bede459f
Reviewed-on: https://vigilo-dev.si.c-s.fr/review/555
Tested-by: Build system <qa@vigilo-dev.si.c-s.fr>
Reviewed-by: Francois POIROTTE <francois.poirotte@c-s.fr>