Remove partitioner/quantizer discussion from readme and link to docs

[metascroy]

To keep information consistent and in-sync, link to CoreML docs rather than discuss the partioner/quantizer.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10033

• 📄 Preview Python docs built from this PR

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

❌ 2 New Failures

As of commit ccc7684 with merge base 9b697ae ():

NEW FAILURES - The following jobs have failed:

• Check Labels / Check labels (gh)
  RuntimeError: Error checking labels: PR does not have required labels
• pull / unittest-arm / linux-job (gh)
  RuntimeError: Command docker exec -t 2f94d2a2537bdfa86f3edcec5de8af6b819106641f0d1dfa865d3bd40a75d964 /exec failed with exit code 1

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[github-actions]

This PR needs a release notes: label

If your changes are user facing and intended to be a part of release notes, please use a label starting with release notes:.

If not, please add the topic: not user facing label.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "topic: not user facing"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.

[metascroy]

@pytorchbot cherry-pick --onto release/0.6 -c docs

[metascroy]

@pytorchbot cherry-pick --onto release/0.6 -c docs

[pytorchbot]

Cherry picking #10033

The cherry pick PR is at #10112 The following tracker issues are updated:

• [v0.6.0] Release Tracker #9253 (comment)

Details for Dev Infra team

Raised by workflow job