[dataimport] add a bit of extra-documentation on the massive store about prepare_insert_relation limitation on inlined relation and lack of full-text indexation.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances