Add tip to install Groovy Eclipse plugin on newer STS versions

CONTRIBUTING.md

@@ -22,6 +22,11 @@ The following provides information on setting up a development environment that
 * Importing the project into Spring Tool Suite
   * File->Import...->Gradle Project
 
+As of new versions of Spring Tool Suite, you might need to install Groovy Eclipse pointing directly to the updates plugin location. To install Groovy Eclipse on Spring Tool Suite based on Eclipse Oxigen you must do the following steps:
+
+Help->Install New Software...->Add the following URL into _Work with_ field:
+http://dist.springsource.org/snapshot/GRECLIPSE/e4.7/
+
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