Dockerfile: ubuntu base image architecture added

[florianlederer]

To build your image on a Rock Pi 4 running an aarch64 architecture I had to add the armhf architecture in the Dockerfile.

[florianlederer]

and by the way thanks for your image!

[ulm0]

Thanks for the PR, thing is i try to use official images since they are up to date, if you're having problems with building this image, you could append --platform=arm to docker build process, or i could modify the scripts for this purpose as well. Let me know

[florianlederer]

@ulm0 Thanks for your response. You're absolutely right. I did not notice that this is an unofficial image. --platform=arm solved my problem.

[ulm0]

Glad it helped! Closing this PR.