On the Beam project, we've got a Jenkins job that stages the site:
https://github.com/apache/beam/blob/master/.test-infra/jenkins/job_beam_PreCommit_Website_Stage.groovy
You can see Jenkins making a comment about where the staged contents are,
as here: https://github.com/apache/beam-site/pull/273.
ASF doesn't support GH Pages, instead you can use a "asf-site" branch
which can be automatically deployed into a web server (fill a ticket
for INFRA)[1]. We use Docker to test changes locally as there is no a
staging option when using Jekyll [2].
[1] https://builds.apache.org/view/S-Z/view/Struts/
