(For the records, this was in the context of #612467 :)
See #612467 for my proposal, which somehow addresses documentation of
the DB creation parts.
Regarding documentation in README.Debian, I guess #612467 is the place
yes.
Now, about db-config use or not : I think it may be very likely that
most users installing spip with Debian packages would expect at least
one default instance to be auto-configured, or installed through the
most minimal set of additional operations needed after apt has
completed.
Most likely, the /ecrire part is unavoidable given that SPIP already
handles this, and things shouldn't be duplicated in the maintainer
scripts.
But creating a DB for the 'default' instance, should, in my opinion, be
made as automatic as possible.
I think a possible way could be to ask in the config, first if the user
wants to create a a DB automatically in MySQL (through db-config),
letting her the option to decline, and proceed manually. That latter
option would then naturally fit the needs of the (most probably fewer)
users needing multi-hosting.
That's the way it is done for fusionforge (if you need a reference
implementation), and suits most cases, IMHO.
Hope this helps.
Best regards,