We publish this page on docs.docker.com, and hugo expects index pages
for sections to be named _index.md. We currently rename the page when we
mount it to the docs repo but might as well change the filename in the
source.
Also adds a linkTitle to the page, which is a shorter title that will be
used in the sidebar navigation and breadcrumbs.
Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>
