Add building instructions

[OLEGSHA]

Describe your use-case which is not covered by existing documentation.

It seems that the repository is set up to be built by the maintainers. However, some users, myself included, may want to build modified versions on the docker image. There are currently no indications on how images might be built manually, and there is no dependency management for building. It would benefit the inexperienced users greatly to document the build command(s) and the tools and dependencies required.

From what I've seen digging around the repository, one should have buildx plugin for Docker, have jq in PATH, and use make build to build a Linux image.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

No response