Add boto3 to requirements.txt (#1745)
Summary:
This PR adds boto3 to the requirements.txt as install.py will error out without it installed.
The README.md list boto3 and pyyaml as packages to be installed before running, but requirements.txt only has pyyaml in the list
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1745
Reviewed By: FindHao
Differential Revision: D46975112
Pulled By: xuzhao9
fbshipit-source-id: db0e3a665c9ea05ea00b059502b1272946d2b648
