Note on limit param in autoPagingToArray

[tvanantwerp]

This change to the README.md file makes it more explicit that the limit value passed to autoPagingToArray is the limit for the total number of items that will be fetched from Stripe, and not a limit for the number of items retrieved per fetch during multiple rounds of fetching. The note about preventing runaway memory growth was suggestive of this behavior, but not entirely explicit.

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[richardm-stripe]

Looks good to me! Sorry for the confusion here.

Also added some comments to the code snippet below to hopefully clarify even further.