Feat: docs: guides: development: upstream monitoring

[tor-announce]: https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-announce

[Tor Forum]: https://forum.torproject.org

[onionspray-announce tag]: https://forum.torproject.org/tag/onionspray-announce

## Upstream monitoring

If you're developing Onionspray, it's recommended to to get alerts on

important upstream announcements:

* For updates on C Tor, follow the [tor-announce][] mailing list.

* Subscribe to the [OpenResty GitHub repository][openresty] to get

  notifications upon releases and security alerts.

[tor-announce]: https://lists.torproject.org/mailman3/postorius/lists/tor-announce.lists.torproject.org/

[openresty]: https://github.com/openresty/openresty