DOC: Use sphinx link for internal link to contributing guide
As requested in #24172.

- [x] closes #24172 

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=h1) Report
> Merging [#24320](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/87e9496fca555e683e388db97b664471bb4a164f?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/24320/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24320   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         162      162           
  Lines       51831    51831           
=======================================
  Hits        47833    47833           
  Misses       3998     3998
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.69% <ø> (ø)` | :arrow_up: |
| #single | `43% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24320?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/24320?src=pr&el=footer). Last update [87e9496...5dd2ebf](https://codecov.io/gh/pandas-dev/pandas/pull/24320?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/24320?src=pr&el=h1) Report
> Merging [#24320](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/87e9496fca555e683e388db97b664471bb4a164f?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/24320/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24320   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         162      162           
  Lines       51831    51831           
=======================================
  Hits        47833    47833           
  Misses       3998     3998
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.69% <ø> (ø)` | :arrow_up: |
| #single | `43% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24320?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/24320?src=pr&el=footer). Last update [87e9496...5dd2ebf](https://codecov.io/gh/pandas-dev/pandas/pull/24320?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks!