[excel] (Samples) Write large dataset clarifications

[AlexJerabek]

As pointed out, this sample was missing a value to enter in one of the Run script blocks. This PR fixes that and adds some clarity in a couple other spots.

[learn-build-service-prod]

Learn Build status updates of commit 2bc6f49:

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docs/resources/samples/write-large-dataset.md	✅Succeeded	View

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[learn-build-service-prod]

Learn Build status updates of commit 44e45a9:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/write-large-dataset-1.png	✅Succeeded	View
docs/images/write-large-dataset-2.png	✅Succeeded	View
docs/images/write-large-dataset-3.png	✅Succeeded	View
docs/images/write-large-dataset-4.png	✅Succeeded	View
docs/images/write-large-dataset-5.png	✅Succeeded	View
docs/images/write-large-dataset-6.png	✅Succeeded	View
docs/images/write-large-dataset-7.png	✅Succeeded	View
docs/images/write-large-dataset-8.png	✅Succeeded	View
docs/resources/samples/write-large-dataset.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel