Correctly redirect to SetupTools documentations
 - [x] closes #16332
 - [x] tests added / passed
 - [ ] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] Correct doc string from http://pythonhosted.org/setuptools to https://setuptools.readthedocs.io/en/latest

@townie Thanks! # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=h1) Report
> Merging [#16333](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1bee0357a97c2c3d79adcd5f120773d7627baca0?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/16333/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16333      +/-   ##
==========================================
+ Coverage   90.37%   90.37%   +<.01%     
==========================================
  Files         161      161              
  Lines       50863    50863              
==========================================
+ Hits        45966    45968       +2     
+ Misses       4897     4895       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.16% <ø> (+0.02%)` | :arrow_up: |
| #single | `40.33% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.59% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16333?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/16333?src=pr&el=footer). Last update [1bee035...654331d](https://codecov.io/gh/pandas-dev/pandas/pull/16333?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/16333?src=pr&el=h1) Report
> Merging [#16333](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1bee0357a97c2c3d79adcd5f120773d7627baca0?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/16333/graphs/tree.svg?height=150&token=eZ4WkYLtcO&width=650&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16333      +/-   ##
==========================================
+ Coverage   90.37%   90.37%   +<.01%     
==========================================
  Files         161      161              
  Lines       50863    50863              
==========================================
+ Hits        45966    45968       +2     
+ Misses       4897     4895       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.16% <ø> (+0.02%)` | :arrow_up: |
| #single | `40.33% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.68% <0%> (-0.35%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.59% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16333?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/16333?src=pr&el=footer). Last update [1bee035...654331d](https://codecov.io/gh/pandas-dev/pandas/pull/16333?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
