Update forced alignment tutorial

[mthrok]

• Fix backtrack visualization (the cooridnate was off-by-one.)
• Add note about the simplification and the new align API
• Explicitly handle SOS and EOS

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/audio/3440

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❌ 2 New Failures

As of commit 90005e9:

NEW FAILURES - The following jobs have failed:

• build (3.8) (gh)
• unittests-windows-gpu / windows-job (gh)

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[facebook-github-bot]

@mthrok merged this pull request in 1860169.

[github-actions]

Hey @mthrok.
You merged this PR, but labels were not properly added. Please add a primary and secondary label (See https://github.com/pytorch/audio/blob/main/.github/process_commit.py).

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