Update Resources/doc/reference/installation.rst
Update Resources/doc/reference/installation.rst

Installation doc updated to use composer
aurelien-vtech/SonataDoctrineORMAdminBundle,pulzarraider/SonataDoctrineORMAdminBundle,pulzarraider/SonataDoctrineORMAdminBundle,rschumacher/SonataDoctrineORMAdminBundle,rschumacher/SonataDoctrineORMAdminBundle,nlzet/SonataDoctrineORMAdminBundle,nlzet/SonataDoctrineORMAdminBundle,sonata-project/SonataDoctrineORMAdminBundle,rschumacher/SonataDoctrineORMAdminBundle,rmzamora/SonataDoctrineORMAdminBundle,nlzet/SonataDoctrineORMAdminBundle,pulzarraider/SonataDoctrineORMAdminBundle,rmzamora/SonataDoctrineORMAdminBundle,nlzet/SonataDoctrineORMAdminBundle,aurelien-vtech/SonataDoctrineORMAdminBundle,rmzamora/SonataDoctrineORMAdminBundle,Bladrak/SonataDoctrineORMAdminBundle,aitboudad/SonataDoctrineORMAdminBundle,rschumacher/SonataDoctrineORMAdminBundle,aurelien-vtech/SonataDoctrineORMAdminBundle