DOC: Creating top-level development section, and moving pages inside
State: closed

- [X] xref #24499
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry


Labels:
name: Docs

Comments:
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=h1) Report
> Merging [#24691](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/decc8ce5601c32dc2313f0d2b1d611164262cae9?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/24691/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24691      +/-   ##
==========================================
- Coverage   92.38%   92.38%   -0.01%     
==========================================
  Files         166      166              
  Lines       52310    52310              
==========================================
- Hits        48327    48326       -1     
- Misses       3983     3984       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (ø)` | :arrow_up: |
| #single | `43.06% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24691/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24691?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/24691?src=pr&el=footer). Last update [decc8ce...95758d1](https://codecov.io/gh/pandas-dev/pandas/pull/24691?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/24691?src=pr&el=h1) Report
> Merging [#24691](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c588437f116a080cdcabb023a5e746dda2cb63c9?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/24691/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24691   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        48425    48425           
  Misses       3988     3988
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `42.89% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24691?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/24691?src=pr&el=footer). Last update [c588437...bbc8713](https://codecov.io/gh/pandas-dev/pandas/pull/24691?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).