Mention MS API Guidelines

[pbrisbin]

https://github.com/microsoft/api-guidelines is a published guidelines we would like to adopt.

Where we have our own guides we mostly align already, and it also provides guidance on some things we don't yet do. Rather than re-invent any wheels, it'd be great to follow something established.

We should mention it in this repository and remove any guides that are conflicting or redundant with it.