Improve output to also incldue mkdocs builds

[charlesreid1]

Per dcppc/use-case-library#95, we should be able to include not just a link to the output log, but a link to the result of mkdocs builds, for relevant tests.

We're currently cloning, building, &c into a temporary directory - this would just require a copy command to copy the site/ folder (or whatever folder) to the /www/archie.nihdatacommons.us/htdocs folder on beavo.

[charlesreid1]

Short term: add a second commit status (test) with a second link to the HTML docs (instead of the output). Then the user gets both links, and we keep both simple.