copied the RFC process from Rust with very slight modifications.

This MR is dedicated to discussing the overall RFC process: when to do it, a basic template, what does accepting an RFC mean.

It is blatantly inspired by the Rust RFC process, however Hathor is not a programming language nor a compiler, so there are some changes required document. However there is a nice parallel, the Hathor protocol and DAG+blockchain structure correspond to the "language", and the hathor-python implementation corresponds to the "compiler".

I think we should keep the process simple and informal. But also keeping in mind that this will eventually go public. For that matter I have no idea what we should do about the license (does being based on the Rust RFC implies choosing a compatible license?).