[mxfp8 moe training] update readme

[danielvegamyhre]

Summary

• MXFP8 training configs and APIs have been updated, and we need to update the docs accordingly
• Link new pytorch blog post on mxfp8 training in the docs

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/4084

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

⏳ 2 Pending, 1 Unrelated Failure

As of commit 2c3d734 with merge base 605a22e ():

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 (CPU Nightly, linux.4xlarge, --pre torch --index-url https://download.pytorch.org/wh... / linux-job (gh) (trunk failure)
  test/quantization/pt2e/test_x86inductor_fusion.py::TestDynamicPatternMatcher::test_q_attention_block

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