Clarify maintenance status

[djc]

I'm no longer motivated to maintain nnpy, and I don't know anyone else who is. Would be good to clarify the maintenance status in the README and/or archive the repo to make this clear to (potential) users. @gdamore any thoughts?

@Ahmadreza-Shahrokhshahi FYI.

[gdamore]

maybe we can add a comment to the table where nanomsg implementations are listed.

can I ask if there is a reason for your change of heart?

[gdamore]

actually as this is just for nanomsg (legacy) you should probably just archive the project. You can add a reference to pynng which is more actively maintained and is built against NNG.

[djc]

can I ask if there is a reason for your change of heart?

It's been five years since I originally wrote the code as a sort of proof of concept, because I thought nanomsg was cool. For myself, I never ended up actually using nanomsg for anything interesting, and on top of that I've mostly stopped writing Python code in favor of writing Rust code. So if I would start using nanomsg/nng again I would probably still not be interested in using this library.

I'll add a note about pynng to the README and archive the repo.