[export_arm_cortexm] Tutorial ``export_lenet_fp32`` make fail

Commit version: 274fc68c

The last part of the tutorial seems to not be up to date

I had to change

!cd lenet_export_fp32 && make build

to

!cd lenet_export_fp32 && make build_image_docker && make build_docker && make

But even after that, the next line:

!./lenet_export_fp32/bin/run_export

Is not good has the export only generates an aidge_stm32.elf. I am not sure if we can test the tutorial using a docker or if there should be instruction on how to push the code to a card ?