Create a copy of the code py file on your NeoTrellis M4 and rename it to something different so you can re-use it later if you want.

Get the python file from here and paste a copy of it on your NeoTrellis M4 board name it code.py

Download or clone the configurator repository

Open up index.html in your browser of choice. 

Click buttons on the left to select coordinates then select a color, add keycodes, and add a comment if you like. Once the key is set as you like click another and configure it as well, continue until you've configured all of the keys that you wan to use.

Click the Export button and copy the keymap dictionary definition from the export text area. Delete the old keymap definition in your code py file, then paste the new one in it's place.