content/2019/playground-v3: add talk on gVisor-based Playgound "v3"

Change-Id: Ib22fbb76a2bd6f99b31a07a570d0a4e169b533ae
Reviewed-on: https://go-review.googlesource.com/c/talks/+/200080
Reviewed-by: Andrew Bonventre <andybons@golang.org>
6 files changed