Add memory info

[astariul]

Great repo !

I think one possibly missing information is the GPU memory used (as a percentage, like for GPU util).

For example sometime my process need only 30% of the memory, so I can start several processes on the same GPU. That would be useful to be able to see the remaining free memory for a given GPU.

[bzamecnik]

Thanks, I'll try to add it when I find some free time for that.