Essentially your Angular code should boil down to one JS file, one CSS file and be hosted in an index.html. If you're dealing with modern browsers a bit of fiddling with the cross domain policy and the withCredentials flag will allow you to host the static assets anywhere (not the same domain as the Rails box).

Otherwise the easiest thing to do is compile into the /public folder of Rails. I wouldn't host in assets as you'll likely be using gulp / grunt so the compilation phase that Rails assets hosting provides will be done for you already.