Update cookbook/security/acl.rst

See https://github.com/doctrine/DoctrineMongoDBBundle/pull/4#issuecomment-8428994
Fixed formatting
add contributing file in the root dir
[#1653] Fixing some mistakes - per @ricardclau
Removing inconsistency in titles in components index page and correcting order
Adding an overview of how the service container concepts fit togther
Fixing some errors in di workflow page
Changed a comment in the examples in the di compilation page
[#1728] Adding a note about a variable that is created in an earlier entry
Merge branch 'making_component_idex_consistent' of git://github.com/richardmiller/symfony-docs into richardmiller-making_component_idex_consistent
Merge branch 'clarifying_compilation_comment' of git://github.com/richardmiller/symfony-docs into richardmiller-clarifying_compilation_comment
Add a cookbook entry to explain how to clear the cache before tests
fixed wrong lines number in book/controller/simple_controller
[reference] Fixing syntax error
Fixing a bad doc reference
Fixing another bad doc reference
fix tiny typo
Further clarifying a sentence in conventions section
Adding some information on normalisation and appending sections in a comfg tree
Fixing indentation issue in components map page