Updated docs to install via composer in dev mode

PHPCS is not used in production, so it fits better in the `require-dev`, avoiding the code be deployed to production environment unnecessarily.
Merge pull request #198 from jrbasso/master

Updated docs to install via composer in dev mode
Fixed bug #20230 : Squiz ControlStructureSpacing sniff assumes specific condition formatting
Merge branch 'master' of https://github.com/squizlabs/PHP_CodeSniffer