Add website update to release process
Update release process with step to get downloads list updated on
containerd.io website
3. Check CI has completed and uploaded the binaries. Remove any binaries which get
uploaded but are not intended as part of the release (e.g. Darwin binaries).
-4. Promote on Slack, Twitter, mailing lists, etc
+4. Update [`config.toml`](https://github.com/containerd/containerd.io/blob/f827d53826a426cb48f24cc08e43cc8722ad6d01/config.toml#L35) with latest release in the [containerd/containerd.io project](https://github.com/containerd/containerd.io); open PR to
+ force website downloads update.
+
+5. Promote on Slack, Twitter, mailing lists, etc
