Sorry for not answering these questions. I recently rebooted the project and yesterday I released a new version [1].
As for the (old) questions. There is no plans to support honeywell. As I understand, it differs too much from DSC it makes little sense to accomodate both systems in the same plugin.
Regarding installation, I've added a section on that in the readme. But it follows the same process as any other NR plugin. The EnvisaLink is connected using 4 wires to the DSC system and then an ethernet cable of course.
There is one input and one output node available.
The input node will send any state updates from the alarm system, including zone triggers even when the alarm is turned off. Therefore, this setup can be used as a presence detector as well.
The output node is used to send commands to the alarm system, like arming or disarming the house.
Feel free to try it out if you run DSC/EnvisaLink and let me know if you have any questions or requests. I'll make sure to answer them this time.