These are the perl files needed, to extend an existing fhem installation with support for the fhemduino.
Just copy all the .pm files from this repository into the fhem/FHEM directory.
If your fhem Installation resides in /opt/fhem, then these files must be copied into the /opt/fhem/FHEM directory.
Connect the fhemduino (Arduino with fhemduino sketch) via usb to your system (Fritzbox, Raspberrypi, ...). Lets assume, it is available as /dev/ttyACM0@9600 then add the fhemduino to your fhem.cfg like this:
define FHEMduino FHEMduino /dev/ttyACM0@9600
Noting to do for you. Let autocreate add the sensors which are received.
Open an issue, and ask.