[doc/book] Add a note about <database>-support virtual package.
Cubicweb setup documentation now mention cubicweb-postgresql-support and cubicweb-mysql-support
#! /bin/sh -e#if [ "$1" = configure ]; then if which install-docs >/dev/null 2>&1; then install-docs -i /usr/share/doc-base/cubicweb-doc fifi#DEBHELPER#exit 0