Integration of Grails into Liferay

Question

I wanted to integrate Grails into a Liferay portlet. I saw that a plugin for that purspose exists (http://www.grails.org/plugin/portlets-liferay) but the documentation is not very helpful.

I only want to start with it, so I create a simple Hello World aplication in Grails (http://grails.org/doc/latest/guide/2.%20Getting%20Started.html#2.4 A Hello World Example) and I want to include it in a Liferay portlet.

Which commands or configuration modifications have I to do?