[Android] update tutorial and provide a SDK setup tutorial

[kirklandsign]

Steps to repro app:

1. Follow https://docs-preview.pytorch.org/pytorch/executorch/2817/getting-started-setup.html to set repo and install requirements.
2. If you haven't set up Java/SDK/NDK already, you can follow https://github.com/pytorch/executorch/blob/170956a8d3e7c811bfd788c15676f3a912779510/examples/demo-apps/android/LlamaDemo/SDK-quick-setup-guide.md to set up them. You can also use Android Studio to install them.
3. Follow https://github.com/pytorch/executorch/blob/7ddd415ed9f375908687da910d9dd1feb429f5dc/examples/demo-apps/android/LlamaDemo/README.md to build the app.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/2879

• 📄 Preview Python docs built from this PR

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

❌ 1 New Failure

As of commit 170956a with merge base 8d8fe09 ():

NEW FAILURE - The following job has failed:

• Apple / upload-frameworks-ios (gh)
  Credentials could not be loaded, please check your action inputs: Could not load credentials from any providers

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[facebook-github-bot]

@kirklandsign has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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@kirklandsign has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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[facebook-github-bot]

@kirklandsign merged this pull request in 3b85946.