[More-than-a-BSP] Registration template

Hi,
I just polished the questions and tried to wrap it into something that
could be used as a template email for the registration, or be linked in
the announcement, which is a bit different. The difficulty is not to
duplicate information while providing enough so that registrants don't
have to re-read the annoucement all the time.

Reviewing welcome ;)

https://wiki.debian.org/BSP/2017/05/fr/Paris/Registration

I'll do the french translation once this version is stabilized.
Cheers,