AWS ML Blog edits

[dougkelly]

• Reduce dataset chunking size for GPU OOM errors
• Typo fixes
• Add explanatory text from blog draft

SageMaker - @philschmid

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[dougkelly]

Closing this PR. Superseded by PR #373 which pins PEFT to v0.2.0 and reverses changes to chunk_length the extra metadata dump from SM Studio.