Add marker files in the root of our tree.
This is needed for publishing in the future:
This is so that we can create a list of directories to ignore when we
rsync documentation builds to a publishing site. Some builds are
published as subdirectories underneath the results of superior
builds.
This allows those superior builds to be rsynced without removing the
other builds that were published under them.
Change-Id: I96a67f022f9fef0794a8a25b6e397177e30d1f5f
9b78b005de