It's available in community applications. If you haven't installed it yet, you should.
I just added "https://github.com/linuxserver/docker-templates" as a docker repository in the unraid docker settings and was able to install tvheadend. Is that correct It looks like it's working
Normally you just install Community application and search and install from there. It's also the preferd way to do it.
Oh right. This thing https://lime-technology.com/forum/index.php?topic=40262.0
thanks, working now.