Update readme to include checkstyle location

Author: patrickfav

README.md

@@ -685,6 +685,12 @@ Use the Maven wrapper to create a jar including all dependencies
 
     mvnw clean install
 
+### Checkstyle Config File
+
+This project uses my [`common-parent`](https://bintray.com/patrickfav/maven/mvn-common-parent) which centralized a lot of
+the plugin versions aswell as providing the checkstyle config rules. Specifically they are maintained in [`checkstyle-config`](https://bintray.com/patrickfav/maven/checkstyle-config). Locally the files will be copied after you `mvnw install` into your `target` folder and is called
+`target/checkstyle-checker.xml`. So if you use a plugin for your IDE, use this file as your local configuration.
+
 ## Tech Stack
 
 * Java 7 (+ [errorprone](https://github.com/google/error-prone) static analyzer)