add cuda doc

[Gasoonjia]

Summary: Add doc for recent introed cuda backend

Differential Revision: D90635397

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16570

• 📄 Preview Python docs built from this PR

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❌ 3 New Failures, 1 Cancelled Job, 1 Unrelated Failure

As of commit 42cc116 with merge base 73c561c ():

NEW FAILURES - The following jobs have failed:

• Lint / link-check / lint-xrefs / linux-job (gh)
  RuntimeError: Command docker exec -t 9ae48826cb13d9c6227d75003ff8e58263e746eb3c6c97d36b8077d27351cc42 /exec failed with exit code 1
• pull / test-static-llama-qnn-linux (stories_110m) / linux-job (gh)
  RuntimeError: Command docker exec -t 7d398a3ca415725296def5d16e8cbb3ce8b6c50c0c61d65033a1b348bb74e174 /exec failed with exit code 9
• pull / test-static-llama-qnn-linux (stories_260k_bc) / linux-job (gh)
  RuntimeError: Command docker exec -t 7cdcebf13d4db3ae5701c1ac4402a1c602c4d8a6238b61c092bba27044b40a94 /exec failed with exit code 9

CANCELLED JOB - The following job was cancelled. Please retry:

• Check Labels (gh)

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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[meta-codesync]

@Gasoonjia has exported this pull request. If you are a Meta employee, you can view the originating Diff in D90635397.

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