Update documentation:formatting for intelliJ (#2511)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8c71783..c29a74e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -67,3 +67,4 @@
 
  - all files must have the Apache license in the header.
  - all PRs must have passing builds for all operating systems.
+ - the code is correctly formatted as defined in the [Scalariform plugin properties](tools/eclipse/scala.properties). If you use IntelliJ for development this [page](https://plugins.jetbrains.com/plugin/7480-scalariform) describes the setup and configuration of the plugin.