add dependencies to setup.py

[caseyjlaw]

There are a handful of pip-installable dependencies that are used by the surveys modules. It is not immediately clear how to install them, so documenting would be helpful. Even better would just be to add them to the setup.py so that they are installed by pip.

[caseyjlaw]

I found the readme in the docs directory, so my first statement was not actually true. Still having that in the README and/or adding all of these requirements to setup.py would be nice.