Add arm64 build to docker image

[fspv]

Hi, I want to run below from a docker image on both x86 and arm machines. Currently github action only builds x86 image.

Docker supports multiarch images, which are created by first publishing two images without a tag (just accessible by a hash) and then merging manifests into one, which references correct manifests for different architectures.

I tested this on my fork and it works. Result: https://hub.docker.com/r/nuhotetotniksvoboden/below/tags

And the correct binaries are compiled:

$ uname -a
Linux devserver 6.8.0-111-generic #111-Ubuntu SMP PREEMPT_DYNAMIC Sat Apr 11 23:16:02 UTC 2026 x86_64 GNU/Linux

$ podman run --rm docker.io/nuhotetotniksvoboden/below --help
Usage: below [OPTIONS] [COMMAND]

Commands:
  live      Display live system data (interactive) (default)
  record    Record local system data (daemon mode)
  replay    Replay historical data (interactive)
  debug     Debugging facilities (for development use)
  dump      Dump historical data into parseable text format
  snapshot  Create a historical snapshot file for a given time range
  help      Print this message or the help of the given subcommand(s)

Options:
      --config <CONFIG>  [default: /etc/below/below.conf]
  -d, --debug
  -h, --help             Print help

$ uname -a
Linux raspberry-pi 6.8.0-1043-raspi #47-Ubuntu SMP PREEMPT_DYNAMIC Fri Oct 17 22:33:56 UTC 2025 aarch64 aarch64 aarch64 GNU/Linux

$ podman run --rm docker.io/nuhotetotniksvoboden/below --help
Usage: below [OPTIONS] [COMMAND]

Commands:
  live      Display live system data (interactive) (default)
  record    Record local system data (daemon mode)
  replay    Replay historical data (interactive)
  debug     Debugging facilities (for development use)
  dump      Dump historical data into parseable text format
  snapshot  Create a historical snapshot file for a given time range
  help      Print this message or the help of the given subcommand(s)

Options:
      --config <CONFIG>  [default: /etc/below/below.conf]
  -d, --debug
  -h, --help             Print help

[meta-cla]

Hi @fspv!

Thank you for your pull request.

We require contributors to sign our Contributor License Agreement, and yours needs attention.

You currently have a record in our system, but the CLA is no longer valid, and will need to be resubmitted.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!