Hi,
Thanks for the super quick reply. I've got it working but had to do a few extra bits as a Raspberry Pi isn't a standard Linux.
I downloaded the lastest Ren'Py SDK (https://www.renpy.org/latest.html) and unzipped it.
I downloaded the Raspberry Pi support file (from the same link). Copied it into the SDK folder and unzipped it.
Then I copied the unzipped NIF folder into the SDK folder.
When running the renpy.sh file NIF now appears as a project and can be launched.
All seems to be working now