Making built image public to facilitate testing

[Utopiah]

Because the result is used on 1 device (RPi4 on LookingGlass Portrait) it would facilitate tinkering to provide an image ready to be dd on a SDcard.

PS: might be done using Github, I was recently positively surprised by how another project, InfiniTime, made both the build working on commit https://github.com/JF002/InfiniTime/blob/develop/.github/workflows/main.yml but also a gitpod available https://github.com/JF002/InfiniTime/blob/develop/.gitpod.yml via Docker to facilitate contributions.