set package name and description for packagist.org

I think this should be a proper symfony distribution, therefor it should be published on packagist.org so it can be installed like this:

    composer create-project jmather/symfony-sonata-distribution demoapp

(https://getcomposer.org/doc/03-cli.md#create-project)

You can log in to packagist with your githun account. The instructions to hook the git repository up to the packagist site are easy as well.