You can find it a bit down the page under "EventBUS"
OpenHAB DOCS BINDINGS
There also a great deal of people, writing in the community about the subject.
The reason I’m doing it like this, is because I have a lot of rules, running my home automation, and I was in a place where turning on a light (IHC) with a presence detector (HUE), could take up to 3-5 sec. So the respond time was growing as I was making rules.
So my current setup is two OH2 PI3, running subscribe/publish via a MQTT broker.
Everything works great, except all my IHC.