Part of https://github.com/ooni/probe-cli/pull/506. In parallel with tutorials, we also need to make sure we have good documentation.
The main tutorial will be the one at https://github.com/ooni/probe-cli/pull/506, but it's useful to also document the primitives used by measurex. So, here's the companion tutorial, which explains how to use the features in netxlite to perform measurements. This work is part of https://github.com/ooni/ooni.org/issues/361.
Original tracking issue for Sprint 41: https://github.com/ooni/probe/issues/1507 Follow-up work in Sprint 42 tracked by: https://github.com/ooni/probe/issues/1689