Add `requirements.txt` file to be used with pip

[Muammar El Khatib]

There is a package called piperqs that automatically generates requirements.txt files:

pipreqs --force /path/to/amp.git

That is convenient because for those installing required python modules with pip, they can do:

pip install -r requirements.txt

The generated requirements.txt is attached to this report. Note that the only requirement not included is TensorFlow because its installation needs other steps.

[andrew_peterson]

We now have a good working pip installer, so this is no longer needed.