After downloading the ubuntu image I had to find a windows machine (windows 7 in my case) because the flash update tool runs under windows and requires even installation of drivers. The documents are terse but the information is there. 1) install the drivers, 2) run the android tool, 3) act on the reprogram switch near the power supply of the Persee (the little hole) until the android tool sees a "Loader" device 4) flash the image.
After flashing ubuntu the system will boot in an ubuntu 14.04 desktop instead of android and you can use that environment to experiment with the persee.
Currently I'm fighting with cross compilation from my linux arch for the Persee (I get ARM executables, but they are just immediately "Killed" when run on the Persee).
I succeeded however in installing ssh and compilers on the persee itself (apt-get update and apt-get install) to be able to compile code for it working from my machine over ssh. Not optimal because compilation on Persee is much slower, but still reasonable.