DOC: fix Dataframe.to_records examples
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Fixed the examples of Dataframe.to_records related to timestamp conversion following the changes in default behaviour made in pull request #18902. As requested in issue #18160.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=h1) Report
> Merging [#22419](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4f11d1a9a9b02a37dbe109d8413cc75d73b92853?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22419/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22419   +/-   ##
=======================================
  Coverage   92.05%   92.05%           
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  Files         169      169           
  Lines       50733    50733           
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  Hits        46702    46702           
  Misses       4031     4031
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <ø> (ø)` | :arrow_up: |
| #single | `42.24% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/22419/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.25% <ø> (ø)` | :arrow_up: |

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=footer). Last update [4f11d1a...140b04e](https://codecov.io/gh/pandas-dev/pandas/pull/22419?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Changes made, as requested.

I also added an example of what happens when the index of the dataframe is given a label. As expected, the attribute of the recarray is named using the label of the index, but I thought it was ambiguous from the docs what might happen. thanks @H0R5E 

@pandas-dev/pandas-core merge on green. Happy to help. Keep up the great work! Thanks for the contribution @H0R5E