Multi-GPU single host training example

Maybe you find the information included in those two threads / sites useful: How to use multiple GPUs on a single node · Issue #69 · jonathan-laurent/AlphaZero.jl · GitHub and GitHub - fabricerosay/AlphaGPU: Alphazero on GPU thanks to CUDA.jl, especially in the first link, however, I have to admit that I am not sure if this is leveraging GPU-to-GPU comms, completely omitting CPUs.