app/config/security.yml : security.acl.connection: default.
symfony_cmf.yml : Fixed missing value for symfony_cmf_create.image.{model,controller}_class

See http://symfony.com/doc/master/cmf/tutorials/installing-configuring-inline-editing.html
DoctrineFixturesBundle : composer.json & AppKernel

See doc. @ http://symfony.com/doc/current/bundles/DoctrineFixturesBundle/index.html
Fixing things following the doc. « Creating a CMS using CMF and Sonata »

See http://symfony.com/doc/master/cmf/tutorials/creating-cms-using-cmf-and-sonata.html

Notably: The content tree seems to work now.
README.md : nothing.
Added app/config/parameters.yml.dist, preconfigured with SQLite as DB backend.