Update README.md

README.md

-# pi-gen
+Forked from [RPi-Distro/pi-gen](https://github.com/RPi-Distro/pi-gen)
 
-_Tool used to create the raspberrypi.org Raspbian images_
+# pi-gen-thymio
+
+_Tool used to create a custom Raspbian image to use Thymio easily_
 
 
 ## Dependencies