Add Sponsors Button to GitHub Repo
While discussion on other support avenues are still ongoing, I think it would still be beneficial to add the a Sponsors Button to the repo that points to https://pandas.pydata.org/donate.html

Note: https://www.flipcause.com/secure/cause_pdetails/MzA3OA== is the direct page to donate but this link doesn't appear as "donate friendly" IMO

Let me know if there's a better link to reference 

Reference to the Support Button on Numpy's page: https://github.com/numpy/numpy/pull/13700

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=h1) Report
> Merging [#26694](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/649ad5c91aabb95d7f200eec84b82cae1459fc65?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/26694/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26694      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         174      174              
  Lines       50701    50701              
==========================================
- Hits        46588    46584       -4     
- Misses       4113     4117       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.41% <ø> (ø)` | :arrow_up: |
| #single | `41.9% <ø> (-0.12%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26694/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26694/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26694?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/26694?src=pr&el=footer). Last update [649ad5c...50b6089](https://codecov.io/gh/pandas-dev/pandas/pull/26694?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/26694?src=pr&el=h1) Report
> Merging [#26694](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/649ad5c91aabb95d7f200eec84b82cae1459fc65?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/26694/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26694      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         174      174              
  Lines       50701    50701              
==========================================
- Hits        46588    46584       -4     
- Misses       4113     4117       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.41% <ø> (ø)` | :arrow_up: |
| #single | `41.9% <ø> (-0.12%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26694/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26694/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26694?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/26694?src=pr&el=footer). Last update [649ad5c...c313b3d](https://codecov.io/gh/pandas-dev/pandas/pull/26694?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 where exactly should the sponsor button appear? Looks like we need to enable it in the "Settings" menu of the repository, but I can't immediately find it:

https://help.github.com/en/articles/displaying-a-sponsor-button-in-your-repository I may not have enough permissions to access the repository settings. Can you enable it @jreback?

<img width="714" alt="Screen Shot 2019-06-07 at 10 23 01 AM" src="https://user-images.githubusercontent.com/10647082/59121976-5891ac00-890e-11e9-96e3-151c4aaa50cc.png">
