Add a release step for specs.opencontainers.org

[sudo-bmitch]

This adds a note to the release process to update specs.opencontainers.org.

[tianon]

We probably need to fix opencontainers/specs.opencontainers.org#8 before this really matters, right?

[tianon]

To put that another way, if we don't get that fixed, this certainly doesn't matter (and we should kill the site instead, perhaps redirecting to GitHub directly or something else that's less than ideal but realistic for our collective ability to maintain it).

[sudo-bmitch]

To put that another way, if we don't get that fixed, this certainly doesn't matter (and we should kill the site instead, perhaps redirecting to GitHub directly or something else that's less than ideal but realistic for our collective ability to maintain it).

I'm fine with this PR being delayed for that. I just wanted to capture it because I didn't realize there was another place we weren't maintaining as part of the release.