DOC: Fixed PeriodArray api ref
[ci skip]

DatetimeArray was listed twice. PeriodArray was missed.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=h1) Report
> Merging [#25526](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/42b4c975e55c59da7868f99f9949841aca12a08d?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/25526/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25526   +/-   ##
=======================================
  Coverage   91.75%   91.75%           
=======================================
  Files         173      173           
  Lines       52960    52960           
=======================================
  Hits        48595    48595           
  Misses       4365     4365
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.33% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25526?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/25526?src=pr&el=footer). Last update [42b4c97...7854a6c](https://codecov.io/gh/pandas-dev/pandas/pull/25526?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/25526?src=pr&el=h1) Report
> Merging [#25526](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b72e7ed320de4d5b9aa8e0b7f2166cee2c7e6fdf?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/25526/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25526      +/-   ##
==========================================
- Coverage   91.26%   91.26%   -0.01%     
==========================================
  Files         173      173              
  Lines       52966    52966              
==========================================
- Hits        48338    48337       -1     
- Misses       4628     4629       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/25526/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3BlcmlvZC5weQ==) | `98.52% <ø> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25526/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.57% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25526?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/25526?src=pr&el=footer). Last update [b72e7ed...895b13d](https://codecov.io/gh/pandas-dev/pandas/pull/25526?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 The linter complained about the ref to `pandas.PeriodIndex`. In the See Also.

I'm not sure if just `PeriodIndex` will give the correct reference to `pandas.PeriodIndex`. It's been a while since I looked at the discovery rules, but I thought that would only work when you're in the same `.. currentmodule`.  I believe that this is inside a `pandas.arrays` currentmodule, so this may fail. We raise when they're both specified but differ.

On Mon, Mar 4, 2019 at 9:28 AM Joris Van den Bossche <
notifications@github.com> wrote:

> *@jorisvandenbossche* commented on this pull request.
> ------------------------------
>
> In pandas/core/arrays/period.py
> <https://github.com/pandas-dev/pandas/pull/25526#discussion_r262107875>:
>
> > @@ -104,13 +104,15 @@ class PeriodArray(dtl.DatetimeLikeArrayMixin, dtl.DatelikeOps):
>          is an ndarray of integers, when `freq` is required. When `values`
>          is a PeriodArray (or box around), it's checked that ``values.freq``
>          matches `freq`.
> +    dtype : PeriodDtype, optional
> +        A PeriodDtype instance from which to extract a `freq`.
>
> Does it override the freq keyword?
>
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>
 > We raise when they're both specified but differ.

Can you then mention this in the docstring you added? thanks @TomAugspurger 