In gh-19928, we recognized that reviewing changes to the website build process (particularly to the tooling) can be labor-intensive:

@jugglinmike if an update like this would break the docs, would we know
without doing a lot of manual work?

Whether or not the resulting website is still acceptable is harder to say,
but maybe not by that much. By building locally, one could compare the
contents of the _build/html directory for both versions of recommonmark.

That is pretty much what I suspected, a lot of manual work could reveal
problems. Building regression testing is tricky if the output often change in
ways that don't matter to users.

So... I guess we just merge and hope.

This patch exposes that information in the continuous integration logs.