docs: use 10e9, not 10e8, for GB Estimate calculation

[rnorth]

@annettejanewilson actually deserves the credit for spotting this 😄

Unless the definition of bytes or GB is unusual, dividing by 10e8 doesn't seem right!

Please follow conventional commit standards
in your commit messages and pull request title.

Give us some context

• What problems does this PR solve?
  • The docs show an incorrect (and thus misleading) example query
• Add any context that will help us review your changes such as testing notes,
  links to related docs, screenshots, etc.
  • Ought to be reasonably self-apparent
• If your issue relates to an existing GitHub issue, please link to it.
  • No it does not.

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[rnorth]

In contact with our legal team about signing the CLA..!

[adutta-newrelic]

Hello @rnorth Could you please update the status of signing the CLA, so that we can go ahead and review this PR.

[rnorth]

Sorry @adutta-newrelic, this is taking longer than I thought! If anybody chose to raise a separate PR to address the issue, I'd be happy to close this one.

I will update here as soon as I'm able to, though.