Improve where docstring
State: closed

A couple small fixes to the `where` docstring, also making an example a bit more clear.

Labels:
name: Docs

Comments:
Changes look good I think failures are from a flaky test so restarted
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=h1) Report
> Merging [#26018](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a1fee9199eba7ebf423880243936b9f1501d3d3a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26018/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26018      +/-   ##
==========================================
- Coverage   91.82%   91.81%   -0.01%     
==========================================
  Files         175      175              
  Lines       52551    52551              
==========================================
- Hits        48256    48252       -4     
- Misses       4295     4299       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.38% <ø> (ø)` | :arrow_up: |
| #single | `40.72% <ø> (-0.14%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `93.54% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=footer). Last update [a1fee91...fd29fc7](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=h1) Report
> Merging [#26018](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a1fee9199eba7ebf423880243936b9f1501d3d3a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26018/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26018      +/-   ##
==========================================
- Coverage   91.82%   91.81%   -0.01%     
==========================================
  Files         175      175              
  Lines       52551    52551              
==========================================
- Hits        48256    48252       -4     
- Misses       4295     4299       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.38% <ø> (ø)` | :arrow_up: |
| #single | `40.72% <ø> (-0.14%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `93.54% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26018/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=footer). Last update [a1fee91...fd29fc7](https://codecov.io/gh/pandas-dev/pandas/pull/26018?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

Thanks @dsaxton