Add a custom JavaScript file to all HTML rendered docs output.
For now it only hosts a small code snipped which gets the current
active section link and bring it into view.
Needs to be triggered after DOM is initially loaded (which is still
before *all* resources like images, iframes, ... are necessarily
loaded), else the query cannot work.
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>