Re-activating the SPIFFE announcement mailing list

[SPIFFE Announce]

Hello - you are receiving this email because you are a member of the `announce` group on spiffe.io. We are writing to let you know that this mailing list is being re-activated, and will be used as a low frequency list for project announcements only. If you do not wish to receive these announcements (~2/month), you may remove yourself from the group by sending an email to the address below. Thanks from being an amazing member of the SPIFFE community!