DOC: Enhancing pivot / reshape docs
- [x] closes #19089 
- [x] tests added / passed (NA Just Docs)
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Enhancing pivot / reshape docs

Added more examples and added Q + A section.
Hello @VincentLa! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on May 16, 2018 at 15:30 Hours UTC I get an error when trying to run

```
(pandas-dev) VincentLa@ch-C02Q6HPBG8WN pandas-vincentla (master) $ git diff upstream/master -u -- "*.py" | flake8 --diff
fatal: bad revision 'upstream/master'
``` @VincentLa do you have your upstream pointing to pandas?

```bash
(pandas_dev) williams-imac:pandas williamayd$ git remote -v show
origin	git@github.com:WillAyd/pandas.git (fetch)
origin	git@github.com:WillAyd/pandas.git (push)
upstream	https://github.com/pandas-dev/pandas.git (fetch)
upstream	https://github.com/pandas-dev/pandas.git (push)
```

If not make sure you do that - it's outlined in the contributing guide:

https://pandas.pydata.org/pandas-docs/stable/contributing.html#forking @WillAyd I believe I do:

```
VincentLa@ch-C02Q6HPBG8WN pandas-vincentla (master) $ git remote -v show
origin	https://github.com/VincentLa/pandas.git (fetch)
origin	https://github.com/VincentLa/pandas.git (push)
upstream	https://github.com/pandas-dev/pandas.git (fetch)
upstream	https://github.com/pandas-dev/pandas.git (push)
``` Hmm have you fetched or pulled anything from upstream yet then? Perhaps `git fetch upstream` will resolve that issue locally? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21038?src=pr&el=h1) Report
> Merging [#21038](https://codecov.io/gh/pandas-dev/pandas/pull/21038?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cf4c0b6164506043c551e95f0036de3ee3eaf2df?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/21038/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21038?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21038   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files         161      161           
  Lines       51200    51200           
=======================================
  Hits        47232    47232           
  Misses       3968     3968
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.63% <ø> (ø)` | :arrow_up: |
| #single | `42.29% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21038?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/21038/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.03% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21038?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/21038?src=pr&el=footer). Last update [cf4c0b6...67112b8](https://codecov.io/gh/pandas-dev/pandas/pull/21038?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback @WillAyd made changes based on the feedback! Would love additional review. can you update can we rebase this @VincentLa (or @datapythonista ) @pandas-dev/pandas-core if someone has a chance to rebase this Updated. Didn't make any changes other than removing whitespace. Updated again, hopefully CI will pass. @jreback this PR is discontinued. Tom and I made changes to it, so it can be merged (some improvements are left as later work, but I think the current version is correct and an improvement to what we have). Otherwise we'll have to close, or keep making the improvements ourselves. thanks @datapythonista 