Provide more guidance for how to create a guest

How to use hyperlight from the host side is pretty simple and there are several examples to help understand. However, when it comes to the guest-side, there is basically only the simpleguest (which first of all is not easy to find in the repo), and it contains mostly testing related code.

We should consider making a guide on how to make and compile guests, and maybe we can provide a template for getting started (one for rust, one for c)?