Add README improvements.
 - [Y] closes #16427 
 - [Y] whatsnew entry
** Included reference to contribute guide in READEME.
** In the "installation from source" section, refer to the actual section in the docs, instead of to the general website
** Update "Discussion and Development" section: remove reference to scipy mailing list, but add one to pandas-dev mailing list
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=h1) Report
> Merging [#16435](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/49ec31bbaeca81a6f58fc1be26fe80f3ac188cdd?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16435/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16435      +/-   ##
==========================================
- Coverage   90.42%    90.4%   -0.03%     
==========================================
  Files         161      161              
  Lines       51023    51023              
==========================================
- Hits        46138    46125      -13     
- Misses       4885     4898      +13
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.23% <ø> (-0.03%)` | :arrow_down: |
| #single | `40.17% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.23% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.05% <0%> (-0.34%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16435?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/16435?src=pr&el=footer). Last update [49ec31b...66f041b](https://codecov.io/gh/pandas-dev/pandas/pull/16435?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/16435?src=pr&el=h1) Report
> Merging [#16435](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/49ec31bbaeca81a6f58fc1be26fe80f3ac188cdd?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/16435/graphs/tree.svg?src=pr&width=650&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16435      +/-   ##
==========================================
- Coverage   90.42%   90.42%   -0.01%     
==========================================
  Files         161      161              
  Lines       51023    51023              
==========================================
- Hits        46138    46137       -1     
- Misses       4885     4886       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.26% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.17% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.23% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16435?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/16435?src=pr&el=footer). Last update [49ec31b...29541b9](https://codecov.io/gh/pandas-dev/pandas/pull/16435?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Are you going to be able to squash them on your end? I'm not sure how to do it once it's already pushed to github. @steven-cutting yeah, we squash and merge. All good @jorisvandenbossche ? 
@jreback @jorisvandenbossche 
With the "contributing" section being added, I feel that the "Discussion and Development" section should change to the "Discussion and Getting Help" section. @steven-cutting I made a small edit and split it just in two separate sections ("Gettting Help" and "Discussion and development")

Thanks for the PR! @jorisvandenbossche 
Excellent, thanks.