Follow the instructions at https://www.docker.com/.
git clone https://github.com/emfcamp/micropython.git
In the micropython directory you just cloned:
docker run --rm -ti -v `pwd`:/opt/micropython davea/tilda-build
It'll take a short while to compile the firmware, and when it's done you'll find firmware.dfu in stmhal/build-STM32L475_EMFBADGE.