Fix #7: Update composer reference to typo3sniffpool

Version 0.0.6 of the package typo3-ci/typo3sniffpool requires version dev-phpcsStandardInstaller
of the package composer/installers. This version doesn't exist anymore. Thus we need another
version of the typo3sniffpool with working requirements.
Fix #7: Update composer reference to typo3sniffpool

Version 0.0.6 of the package typo3-ci/typo3sniffpool requires version dev-phpcsStandardInstaller
of the package composer/installers. This version doesn't exist anymore. Thus we need another
version of the typo3sniffpool with working requirements.
Adapt documentation accordingly.
Merge pull request #8 from skorpi/sniffpool-version

Fix #7: Installation of 1.0.0-alpha failed