Mailing list migration to mailman3

[Sergey Budnevitch]

	Hello,

As you may noticed already mailing list was migrated to mailman3. It differs significantly from mailman2 we used previously.
Please pay attention to a few noticeable changes:

 * Mailman3 does not add X-BeenThere header to the outbound emails anymore. If you used this header for your filters, you should switch to the List-Id header (or List-Post header).
 * Old archives are available on https://mailman.nginx.org/pipermail/, New archives started on Jan 1 2020 and could be found on https://mailman.nginx.org/mailman3/lists/
 * mail interface for subscribing/unsubscribing works as before, but web interface and authorisation have changed. To get access to the web interface you need to "sign up" with your email address, "reset password" will not work as technically there is no web user yet.