Coding: add requirements.txt

[chrisroederucdenver]

Add a requirements.txt to make it easier to create an environment with required libs.

[callahantiff]

Hey @chrisroederucdenver - thanks for your issue. The requirements are stored in the setup.py file. If you download the library from PyPI it should handle this part for you.

[chrisroederucdenver]

Thanks. I cloned from git, created a new venv and then went to pip install. The -r flag on pip, if you have a requirements.txt, makes that step a little simpler and shorter. I'll submit a pull request updated with the same versions there.