Just a quick post to helpfully save people some time.
When I followed the instructions yesterday on my OH2.5 snapshot version I noticed that when OH loaded my rule file, the rule would fail to be parsed with a NoClassDefFoundError (at least I think that was the correct exception name).
If you get this error, my tip would be to ensure when you download the JS libs, you make sure you use the smarthome-To-openhab.core branch.
Details of how to clone the repo can be found above in @rlkoshak’s post. Doing so will enable you to quickly update (git pull) and switch branches (git checkout -b smarthome-To-openhab.core) as necessary..