Update quantization README.md

[vkuzo]

Updating quantization README with updated benchmark results from #3473, and deleting the old outdated benchmarks

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/3551

• 📄 Preview Python docs built from this PR

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 26845e9 with merge base 886ac8e ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Run Regression Tests / test-nightly (CUDA Nightly, linux.g5.12xlarge.nvidia.gpu, --pre torch --index-url https://downloa... / linux-job (gh) (trunk failure)
  test/test_low_bit_optim.py::TestFSDP2::test_fsdp2

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