Update installation.rst
Update installation.rst

Adding information due to some errors e.g.
The child node "templates" at path "sonata_page" must be configured.
The child node "multisite" at path "sonata_page" must be configured.
The child node "default_template" at path "sonata_page" must be configured.
Dunduro/SonataPageBundle,grimpows/SonataPageBundle,Th3Mouk/SonataPageBundle,grimpows/SonataPageBundle,Th3Mouk/SonataPageBundle,Aylarius/SonataPageBundle,Aylarius/SonataPageBundle,Dunduro/SonataPageBundle,Aylarius/SonataPageBundle,Th3Mouk/SonataPageBundle,Aylarius/SonataPageBundle,grimpows/SonataPageBundle,Dunduro/SonataPageBundle,grimpows/SonataPageBundle,Dunduro/SonataPageBundle,sonata-project/SonataPageBundle,Dunduro/SonataPageBundle,Th3Mouk/SonataPageBundle,sonata-project/SonataPageBundle,grimpows/SonataPageBundle,Aylarius/SonataPageBundle