[Contributing] New PR and commit reqs.

Introducing new pull request and commit requirements.
Title typo
Merge pull request #431 from TheMelter/master

Title typo
Fixed grammar.
Merge pull request #432 from TheMelter/master

Fixed grammar.
Update getting-started.rst

Doctrine\Bundle\PHPCRBundle\Initializer\GenericInitializer has two required parameters.
What do you think ?
Merge pull request #433 from benoitMariaux/patch-2

Update getting-started.rst
Fixed mismatching namespace
Merge pull request #434 from TheMelter/master

Fixed mismatching namespace
Grammar fix for ChainRouter page
Nexted navigation fix
Merge pull request #435 from TheMelter/master

Grammar fix for ChainRouter page, nested navigation fix
documentation for cleaned up routing
Update auto-routing.rst
Merge pull request #437 from benoitMariaux/patch-3

Update auto-routing.rst
documenting the limit on candidates
adjust for simplecms routing refactoring
improve mediabundle documentation
Merge pull request #440 from symfony-cmf/media-doc

improve mediabundle documentation
make comment on limit_candidates a caution