Add ARM CMSIS project template references to documentation

[rascani]

Summary

Link to Arm-Examples/cmsis-executorch and Arm-Examples/cmsis-zephyr-executorch repositories, which provide alternative project structures for deploying ExecuTorch on ARM embedded systems with CMSIS tooling.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17454

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 22dfc69 with merge base c12dc35 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 89aa03cc87b81da65eff5f010402a149a3c930f6d359eebbcdde07192bacb9e0 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t fb73d2e345817ab14a4d27a8547c716625eb8acddaef402022f8310aa3506f5f /exec failed with exit code 1

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / unittest-release / windows / windows-job (gh) (detected as infra flaky with no log or failing log classifier)

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