Add function to find Rigaya encoder binaries

[anne-o-pixel]

Hello

On my Archlinux, NVEncC is not found:

python3 -c "
import shutil
print('nvencc:', shutil.which('nvencc'))
print('NVEncC:', shutil.which('NVEncC'))
"

give me

nvencc: /usr/bin/nvencc
NVEncC: None

So even if I had nvenc, I was using ffmpeg_hevc_nvenc
With my change, it's avoid me doing sudo ln -s /usr/bin/nvencc /usr/local/bin/NVEncC

[cdgriffith]

Thank you for the great addition!