Add requirement for a 1-dimensional ndarray in the `pd.qcut` docstring
- [x] closes #18173 

`pd.qcut` only accepts 1-dimensional numpy arrays, which is not mentioned in the docstring. This PR  updates the docstring accordingly.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=h1) Report
> Merging [#18211](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/324ac85cda1ebc37ecd2e450df407ffba83eed8a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18211/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18211      +/-   ##
==========================================
+ Coverage    91.4%    91.4%   +<.01%     
==========================================
  Files         163      163              
  Lines       50064    50064              
==========================================
+ Hits        45760    45763       +3     
+ Misses       4304     4301       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.21% <ø> (+0.02%)` | :arrow_up: |
| #single | `40.36% <ø> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/tile.py](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS90aWxlLnB5) | `90.25% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.2% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18211?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/18211?src=pr&el=footer). Last update [324ac85...890e010](https://codecov.io/gh/pandas-dev/pandas/pull/18211?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @jdoepfert  thx @jreback !