Update README with how-to apply for modules.
Update README with how-to apply for modules.

Added documentation how-to apply plugin for project modules using new Gradle plugins api.

Signed-off-by: Yahor Berdnikau <65de286607a8090de37d6bb23a427517fd3c474e@gmail.com>

JLLeitschuh/ktlint-gradle,JLLeitschuh/ktlint-gradle