[RPKI] RPKI Discord server

[Alex Band]

Dear RPKI list,

We are now also offering a Discord server dedicated to RPKI. 

This is the invite link:
https://discord.gg/NY5SWeJzec

We think Discord invites a different type of discussion and consider it a good addition to, and certainly not a replacement of, this mailing list.

The NLnet Labs code of conduct applies to the use of this service:
https://www.nlnetlabs.nl/conduct/

On behalf of the NLnet Labs team,

Alex