README could use some updates

[sparticlesteve]

should update the data stuff since the pre-splitting is now done. Probably still useful to keep the splitting instructions for anyone that might be using the previous non-split data.

should probably add a brief note about installing mlperf-logging

[sparticlesteve]

should also mention the LR warmup package

[azrael417]

I updated the readme about the preprocessing. Maybe I should add a requirements.txt, what do you think?

[sparticlesteve]

Looks good. Might just want to mention mlperf-logging.

i guess some folks may appreciate a requirements.txt file. Your call.