docs: code samples for DataFrame.rename, Series.rename

[shobsi]

BEGIN_COMMIT_OVERRIDE
docs: code samples for rename , size (#293)

docs: code samples for Series.{name, std, agg} (#293)
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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)
  • DataFrame.size: https://screenshot.googleplex.com/55MHXNuAamdfbud
  • Series.size: https://screenshot.googleplex.com/5ve4T8UJq2TUiWb
  • DataFrame.rename: https://screenshot.googleplex.com/7eWsfcz8tmLx4pY
  • Series.rename: https://screenshot.googleplex.com/3HbXTxCaJVsbEzs
  • Series.name: https://screenshot.googleplex.com/7FpNDWJEyiqGLpN
  • Series.std: https://screenshot.googleplex.com/4RSTC8s2tYYK5cW
  • Series.agg: https://screenshot.googleplex.com/63TmACx23TPJu2K

Fixes internal issues 317997641 and 317998300 🦕