docs: add code samples for values and value_counts

[shobsi]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
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• Appropriate docs were updated (if necessary)
  • Series.values: https://screenshot.googleplex.com/KT92XeinGR7ESdt
  • Series.value_counts: https://screenshot.googleplex.com/3GWfDqryzcAnfn9
  • DataFrame.value_counts: https://screenshot.googleplex.com/4XJLbZ9Tg8GpVNG

Fixes internal issue 314161081 🦕

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[ashleyxuu]

Thanks.

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