This pull request publishes the step-by-step design document that I have been discussing with @hellais and @DecFox recently. Compared to the document that was approved, this one has been edited for readability.
While there, I figured it was also be beneficial to publish the few ooni/probe-cli related design documents we produced in the past, because they probably help someone to get acquainted with the codebase.
Reference issue for this pull request: https://github.com/ooni/probe/issues/2148
