DOC: fix wrongly placed versionadded
Just came across a wrongly placed versionadded tag
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=h1) Report
> Merging [#16702](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b7e7fd3f17d4d2a2f87b9d169cf87143f04e5d33?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/16702/graphs/tree.svg?height=150&src=pr&token=eZ4WkYLtcO&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #16702   +/-   ##
=======================================
  Coverage   90.91%   90.91%           
=======================================
  Files         161      161           
  Lines       49286    49286           
=======================================
  Hits        44810    44810           
  Misses       4476     4476
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.69% <ø> (ø)` | :arrow_up: |
| #single | `40.17% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.48% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16702?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/16702?src=pr&el=footer). Last update [b7e7fd3...d245035](https://codecov.io/gh/pandas-dev/pandas/pull/16702?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/16702?src=pr&el=h1) Report
> Merging [#16702](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b7e7fd3f17d4d2a2f87b9d169cf87143f04e5d33?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/16702/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #16702   +/-   ##
=======================================
  Coverage   90.91%   90.91%           
=======================================
  Files         161      161           
  Lines       49286    49286           
=======================================
  Hits        44810    44810           
  Misses       4476     4476
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.69% <ø> (ø)` | :arrow_up: |
| #single | `40.17% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.48% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16702?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/16702?src=pr&el=footer). Last update [b7e7fd3...d245035](https://codecov.io/gh/pandas-dev/pandas/pull/16702?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. side issue: seems doc build is having issues

@TomAugspurger  Maybe related to sphinx 1.6? I tried to build with 1.6 when it was released and it worked but seemed to take a while. I'll do some timings.  Something with the autosummary / autodoc is going wrong (all classes warn about methods with unknown toctree references, a problem we have had before), and indeed started going wrong since sphinx 1.6.

Might be that the big timing is just due to the gigantic amount of warnings (log is too large for travis, that's why it stopped).

But we need to fix the autodoc anyway. Will do a PR to fix sphinx to 1.5 for now. Made a PR to pin for now, and an issue to track the problem: https://github.com/pandas-dev/pandas/issues/16705