Update docs for simple usage of scripts/build_apple_frameworks.sh

[jathu]

Summary

After #11115, we don't need to pass all the flags.

Test plan

rg "build_apple_frameworks" -t markdown

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/11174

• 📄 Preview Python docs built from this PR

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✅ You can merge normally! (2 Unrelated Failures)

As of commit 820d3e2 with merge base bfdbd5b ():

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

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  examples/models/llama/tests/test_export_llama_lib.py::ExportLlamaLibTest::test_has_expected_ops_and_op_counts
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  examples/models/llama/tests/test_export_llama_lib.py::ExportLlamaLibTest::test_has_expected_ops_and_op_counts

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