Improve benchmarks shown on the readme.md page

[ahmadsharif1]

We should:

1. Use a real video instead of a synthetic one (or use a fractal video so there is some motion).
2. Benchmark throughput using a dataloader
3. Benchmark cuda decoding
4. Benchmark comparing against other decoders like decord
5. Benchmark different ffmpeg versions
6. Benchmark different encoding formats
7. Use one legend instead of multiple
8. Maybe stack the bars vertically?
9. Show machine information like # of cpu cores, etc.