docs: code samples for Series.{map, to_list, count}

[shobsi]

BEGIN_COMMIT_OVERRIDE
docs: code samples for Series.{map, to_list, count} (#290)

docs: code samples for DataFrame.copy and Series.copy (#290)
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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
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
  • Series.map: https://screenshot.googleplex.com/BNZNjfhpRQobgZY
  • Series.to_list: https://screenshot.googleplex.com/9mADuEgs9SXToSj
  • Series.count: https://screenshot.googleplex.com/5tvzAfZWGaQV9AW
  • Series.copy: https://screenshot.googleplex.com/C7FzyPLrmfJ4qDx
  • DataFrame.copy: https://screenshot.googleplex.com/6wfFrxLqwRPKMqW

Fixes internal issues 317829931 and 317829933 🦕