Documentation Guides

python-can could really do with a few [documentation guides](https://docs-guide.readthedocs.io/en/latest/doctypes/) to compliment the example code and reference docs.

> Guides are meat of documentation and they should:
> - be comprehensive,
> - show vast majority of possible options (but should not show all possible options -- that is the task for reference),
> - show how all concepts fit together,
> - answer the question "why?".