Mediapipe Version Updated

Mediapipe 0.10.1 is no longer available via PyPI it seems. I have updated the pinned version to the most recent available patch (0.10.20) which tests successfully across Windows/Linux/MacOS.

My recollection is that there were patches of Mediapipe 0.9 that failed on MacOS (some worked, some did not). Uneasiness about this led me to pin to a specific patch that I knew worked.

JOSS Release

v0.5.1

Update README.md