DOC: Creating top-level getting started 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/24678?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@caf462c`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24678/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24678?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #24678   +/-   ##
=========================================
  Coverage          ?    90.8%           
=========================================
  Files             ?      166           
  Lines             ?    52327           
  Branches          ?        0           
=========================================
  Hits              ?    47515           
  Misses            ?     4812           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (?)` | |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24678?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/24678?src=pr&el=footer). Last update [caf462c...a2c0a69](https://codecov.io/gh/pandas-dev/pandas/pull/24678?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/24678?src=pr&el=h1) Report
> Merging [#24678](https://codecov.io/gh/pandas-dev/pandas/pull/24678?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/14eac280e1b7516714d117e65b45023dee7feee7?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/24678/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24678?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24678   +/-   ##
=======================================
  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/24678?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/24678?src=pr&el=footer). Last update [14eac28...6474b5f](https://codecov.io/gh/pandas-dev/pandas/pull/24678?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).