You can clone with
HTTPS or Subversion.
TernJs doesn't show in a list for installed packages. It is not in https://sublime.wbond.net/repositories.json list too. For now I just manually added "https://github.com/emmetio/sublime-tern" as a repository through PM.
It’s not officially announced yet so it’s not in Package Control.
Ah sorry, do you need any issue reports or it is too early? :)
Also - thank you for this plugin!
Issues like #5 you should address directly to @marijnh at https://github.com/marijnh/tern