Added README on running the code on DGX Spark, and DGX Spark recipes

[weehyong]

What does this PR do

Related issue

Which chapter or area does this touch

How to test

# example
cd code
pytest chapter05/tests -q

Checklist

• Tests added or updated for the change (if it's a bug fix or behavior change)
• pytest -q passes from code/
• ruff check . passes from code/
• README or chapter README updated if user-facing instructions changed
• No secrets, API keys, or personal data in the diff
• No large binary artifacts (model checkpoints, training runs) in the diff
• The change does not alter file paths the book references in listings

Additional context

[weehyong]

Added files, and updates to include DGX Spark testing of the code for the book