[Android] Update instructions for build types

[kirklandsign]

Stack from ghstack (oldest at bottom):

• (to be filled)

User can use export EXECUTORCH_CMAKE_BUILD_TYPE=Debug

Differential Revision: D64795144

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/6446

• 📄 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 cc70d3d with merge base fe20be9 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
  ##[error]No files were found with the provided path: /home/ec2-user/actions-runner/_work/_temp/artifacts/. No artifacts will be uploaded.
• Propose to merge ghstack orig PRs to main / Try to create a PR with ghstack /orig branch (gh)
  github.GithubException.GithubException: 404 {"message": "Branch not found", "documentation_url": "https://docs.github.com/rest/branches/branches#get-a-branch", "status": "404"}

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