Write a style guide

Whilst we follow PEP8, there are more general style questions that we do not have written down. Particularly relevant to people coming from Java are things like when to use objects and when to use getters/setters. We should write a guide to this that highlights major differences in style when coming from Java.

## Acceptance Criteria
* There is a style guide in the docs that covers some of these broader questions

## Notes
* I would personally just link to https://google.github.io/styleguide/pyguide.html. I think I agree with most of it and saves us having to write something or argue over it. I think it would still be good to just highlight some of the major differences to java next to that link though