DOC: improved docstring for pandas.pivot

[irruka]

Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

• [Y] PR title is "DOC: update the docstring"
• [Y ] The validation script passes: scripts/validate_docstrings.py <your-function-or-method>
• The PEP8 style check passes: git diff upstream/master -u -- "*.py" | flake8 --diff
• The html version looks good: python doc/make.py --single <your-function-or-method>
• [Y ] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

# paste output of "scripts/validate_docstrings.py <your-function-or-method>" here
# between the "```" (remove this comment, but keep the "```")

If the validation script still gives errors, but you think there is a good reason
to deviate in this case (and there are certainly such cases), please state this
explicitly.

[pep8speaks]

Hello @irruka! Thanks for submitting the PR.

• In the file pandas/core/reshape/reshape.py, following are the PEP8 issues :

Line 410:1: E101 indentation contains mixed spaces and tabs
Line 410:1: W191 indentation contains tabs
Line 410:1: W293 blank line contains whitespace
Line 411:1: E101 indentation contains mixed spaces and tabs
Line 412:1: E101 indentation contains mixed spaces and tabs
Line 412:1: W191 indentation contains tabs
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Line 414:35: W291 trailing whitespace
Line 424:1: E101 indentation contains mixed spaces and tabs
Line 424:1: W191 indentation contains tabs
Line 424:1: W293 blank line contains whitespace
Line 425:1: W191 indentation contains tabs
Line 428:1: E101 indentation contains mixed spaces and tabs
Line 428:1: W191 indentation contains tabs
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Line 431:1: E101 indentation contains mixed spaces and tabs
Line 434:1: E101 indentation contains mixed spaces and tabs
Line 434:1: W191 indentation contains tabs
Line 435:1: W191 indentation contains tabs
Line 435:1: W293 blank line contains whitespace
Line 436:1: W191 indentation contains tabs
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Line 438:1: W293 blank line contains whitespace
Line 439:1: W191 indentation contains tabs
Line 439:77: W291 trailing whitespace
Line 440:1: W191 indentation contains tabs
Line 441:1: W191 indentation contains tabs
Line 441:1: W293 blank line contains whitespace
Line 442:1: W191 indentation contains tabs
Line 443:1: E101 indentation contains mixed spaces and tabs
Line 445:1: E101 indentation contains mixed spaces and tabs
Line 445:1: W191 indentation contains tabs
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Line 446:1: W293 blank line contains whitespace
Line 447:1: W191 indentation contains tabs
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Line 450:1: W293 blank line contains whitespace
Line 451:1: W191 indentation contains tabs
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Line 454:1: W191 indentation contains tabs
Line 454:29: W291 trailing whitespace
Line 455:1: W191 indentation contains tabs
Line 455:1: W293 blank line contains whitespace
Line 456:1: W191 indentation contains tabs
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[jorisvandenbossche]

@irruka There was apparently also another PR updating pandas.pivot, which has been merged in the meantime: #20250 (I hope this was not due to an error in the docstring assignment from our side, in that case: sorry!)
Can you check the other PR, and see if you have changes in this PR that would still be further improvements compared to what has been merged? And if that is the case, feel free to open a new PR!

[alimcmaster1]

@jorisvandenbossche think we should be okay to close this given we havn't heard back from @irruka and looks like this was largely addressed in #20250 . @irruka please feel free to re-open if you think otherwise/have any further improvements.