enable running a model script directly

[wconstab]

right now, you can't python torchbenchmark/models/dlrm/__init__.py becuase "ImportError: attempted relative import with no known parent package".

how can the main block in init.py be executed? If it's possible we should write up the workaround in README, or else it would be nice to enable.

[Krovatkin]

I think this python -m torchbenchmark.models.BERT_pytorch.__init__ works pretty well now, but we should add it to README.md

[xuzhao9]

I think this python -m torchbenchmark.models.BERT_pytorch.__init__ works pretty well now, but we should add it to README.md

The command works for the BERT_pytorch model, but when I am running it on other models, say "Background_Matting", the command returns nothing because there is no main function in the module: https://github.com/pytorch/benchmark/blob/master/torchbenchmark/models/Background_Matting/__init__.py