Add usage guidelines and documentation

[codebytere]

As it stands, the requisite formatting needed to make various parts of Electron's documentation type in specific ways remains tribal. Unless you work with Electron constantly, it's not intuitive or clearly laid out that, for example, one would need to say something like:

`MyDopeParam` String - Can be `a`, `b`, or `c`.

in order to have a string param type as a string literal. We should at the very least begin to incrementally centralize this knowledge to reduce friction for those who many want to contribute to our docs or otherwise work on the project.

[MarshallOfSound]

This should probably be added to https://github.com/electron/electron/blob/master/docs/styleguide.md which has a lot of info around our docs style 👍