Add accelerate to requirements.txt (#849)
Summary:
Used by `torchbenchmark.e2e_models.hf_bert`
```
File "/raid/shenli/benchmark/torchbenchmark/e2e_models/hf_bert/__init__.py", line 9, in <module>
from accelerate import Accelerator
ModuleNotFoundError: No module named 'accelerate'
```
Pull Request resolved: https://github.com/pytorch/benchmark/pull/849
Reviewed By: ejguan
Differential Revision: D35362807
Pulled By: xuzhao9
fbshipit-source-id: c0990d23c1e43cf873a72bbc38adbec51f3b9f91
