The .php_cs
file is used for the GitHub pre-commit static reviews.
Magento 2 uses the sjparkinson/static-review
library for Git pre-commit hooks: http://www.sitepoint.com/writing-php-git-hooks-with-static-review/
vendor/bin/static-review.php hook:install dev/tools/Magento/Tools/StaticReview/pre-commit .git/hooks/pre-commit