Documentation for using Docker with builds.apache.org

[Daniel Takamori <po...@apache.org>]

Hello Docker friends,
Our documentation at http://wiki.apache.org/general/Jenkins doesn't have
any mention of our support for Docker, nor any hints about how to use it.
While currently on MoinMoin (wiki.a.o) we'll start adding newer docs on
reference.a.o.
If anyone who is currently using docker for their builds has an examples
they wouldn't mind documenting, I've put up a page that they can be added
to https://reference.apache.org/committer/jenkins-docker

Much appreciated on behalf of Infra,
-Pono