Every month, streaming services add dozens of new TV shows and movies to their libraries. They do this in order to keep their old subscribers around and entice new ones into signing up. But no matter how exciting these additions may be, there are far too many services for any of us to subscribe to them all. Thankfully, paid services aren’t the only choices — many free alternatives have started popping up all over. One of the best options is The Roku Channel, and the service is adding a bunch of free movies to its library in December. The Roku…