add a step in the documentation for non programmers like me

[kwyjiboo]

Hi
Thank you for you great work.
I followed your readme file for the installation with Hassio and had an issue where the duofern was not initialized properly. After looking around in the code I found that in the init python file two lines were mentioning /dev/serial/by-id/usb-Rademacher_DuoFern_USB-Stick_WR04ZFP4-if00-port0
but in the gui in the hardware tab mine said /dev/serial/by-id/usb-Rademacher_DuoFern_USB-Stick_WR029BQK-if00-port0.

I replaced these two mentions with the one I got and it's working like a charm.

Maybe add this step in your documentation so that other n00bs like me don't search what they did wrong for hours.

Keep up the good work and thanks again