third-party dependency

[zeng-zc]

It's seems a great job.
When I install it by pip install alphavideo under ubuntu 14.04, I found it depends on cuda, pytorch and others. I advice to add these dependency in the README.

By the way, can you supply a CPU version without CUDA for trial?

[zeng-zc]

If there is a Docker container, it would be very easy for a tiral. Thank you very much!