sig-release: Create release-comms list (external release communications)
sig-release: Create release-comms list (external release communications)

We've had a comms snafu or two in past release cycles.
This list is to ensure multiple Release Team members and SIG Release
representatives are in the feedback loop when communicating to external
stakeholders, like the CNCF, to provide additional context, identify
potential gaps, and miscommunications.

release-comms@ currently includes:
- 1.18 Release Team Lead & Lead Shadows
- 1.18 Communications Lead & Comms Shadows
- SIG Release Chairs

Signed-off-by: Stephen Augustus <f96984fef9637085f0559f1484dfd4e99545cd6e@vmware.com>

thockin/k8s.io,thockin/k8s.io,thockin/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,kubernetes/k8s.io,thockin/k8s.io,kubernetes/k8s.io