Contribution: TuxMake + TuxRun bisection workflow (Anders/Ben)

[bhcopeland]

Anders and Ben to share the TuxMake + TuxRun reproducible bisection
workflow.

This is the approach from the Linaro blog posts — use TuxMake for
reproducible builds in containers and TuxRun for QEMU-based testing,
driven by git bisect run. Keeps the compiler, config, and runtime
environment fixed so only the source changes between steps.

Ben is also working on getting TuxMake into KernelCI proper, which
feeds directly into this.

Drop scripts/examples into contrib/tuxmake-tuxrun/ with a README.