Guidance paper on How to add an API to the LTS version

We will have situations where teams want to add APIs to the LTS version. This will then, in the future need to be ported to the WASI P2+ / CM based WIT world. How do we support folks who need to do this?

We should provide a guidance paper, a quick, short document which provides a solution. In a discussion with @lukewagner it was suggested that this could be done using core-Wasm data types and expressed the way the current core APIs are. However, we should provide guidance on how these can be translated into WIT when the time comes.

We should record this advice in a document.