main.py --test-all fails due to missing cv2 dependency

[cedarhillgoods]

The readme is missing the opencv package as a dependency, causing --test-all to fail.

$ ./main.py --test-all Traceback (most recent call last): File "./main.py", line 9, in import cv2 ImportError: libhdf5.so.103: cannot open shared object file: No such file or directory