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.
Update installation.rst

RoutingBundles were missing
Updated CSS for Sonata Demo menu
Upadted CSS
Merge pull request #230 from Bladrak/demoMenuCss

Updated CSS for Sonata Demo menu
Merge pull request #224 from zodysaidoo/patch-1

Update installation.rst
Merge pull request #227 from zodysaidoo/patch-2

Update installation.rst
Symfony 2.4 compatibility
Merge pull request #231 from peterkokot/patch-1

Symfony 2.4 compatibility added
Merge branch 'sonata/master'

Conflicts:
	composer.json