Write documentation for the user-facing functions

[tholop]

Where?

Things to document in priority:

• The Python interface used by Syft 0.2.x (and soon SyMPC): https://github.com/OpenMined/sycret/blob/master/sycret/fss.py (basically just the keygen and eval functions)
• Improve the Readme

Later:

• The important Rust primitives

Who?

• Anyone doing pip install sycret should be able to read the doc to use fss.py
• The rest of the documentation will be useful for contributors and maintainers

What?

Let's use Google-style Python docstrings (https://github.com/OpenMined/SyMPC/issues/28). It can be cool to plug a static documentation website builder into the workflow :grin:

[nph4rd]

I'd like to take this one!

[tholop]

Awesome, thanks! Feel free to leave some gaps or ping me if some parameters or functions are unclear.