README: point Kotlin users to external guide #470

Author: vapier

README.md

@@ -45,7 +45,9 @@ encourages you to share these documents. See
 [https://creativecommons.org/licenses/by/3.0/][ccl] for more details.
 
 The following Google style guide lives outside of this project:
-[Effective Dart][dart].
+
+*  [Effective Dart][dart]
+*  [Kotlin Style Guide][kotlin]
 
 ## Contributing
 
@@ -70,6 +72,7 @@ primarily optimizing for Google's internal needs.
 [gh-tracker]: https://github.com/google/styleguide/issues
 [go]: go/
 [java]: https://google.github.io/styleguide/javaguide.html
+[kotlin]: https://developer.android.com/kotlin/style-guide
 [py]: https://google.github.io/styleguide/pyguide.html
 [r]: https://google.github.io/styleguide/Rguide.html
 [sh]: https://google.github.io/styleguide/shellguide.html