DOC: improved pivot_table(..) aggfunc parameter explanation
- [ ] closes #18712 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @stefansimik! Thanks for updating the PR.



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

##### Comment last updated on December 12, 2017 at 11:15 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=h1) Report
> Merging [#18718](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1c1f5076173c590ed9b19992679305bc70c7956c?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18718/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18718      +/-   ##
==========================================
- Coverage   91.58%   91.57%   -0.02%     
==========================================
  Files         153      153              
  Lines       51305    51307       +2     
==========================================
- Hits        46989    46982       -7     
- Misses       4316     4325       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.43% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.71% <ø> (-0.1%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <ø> (-0.1%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.84% <0%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18718?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/18718?src=pr&el=footer). Last update [1c1f507...1cc42d3](https://codecov.io/gh/pandas-dev/pandas/pull/18718?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/18718?src=pr&el=h1) Report
> Merging [#18718](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1c1f5076173c590ed9b19992679305bc70c7956c?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18718/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18718      +/-   ##
==========================================
+ Coverage   91.58%   91.59%   +<.01%     
==========================================
  Files         153      153              
  Lines       51305    51364      +59     
==========================================
+ Hits        46989    47047      +58     
- Misses       4316     4317       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.45% <ø> (+0.02%)` | :arrow_up: |
| #single | `40.74% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <ø> (-0.1%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/io/parquet.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnF1ZXQucHk=) | `60.19% <0%> (-5.2%)` | :arrow_down: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.55% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `93.8% <0%> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `95.9% <0%> (ø)` | :arrow_up: |
| [pandas/tseries/offsets.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvb2Zmc2V0cy5weQ==) | `96.95% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.43% <0%> (ø)` | :arrow_up: |
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.84% <0%> (ø)` | :arrow_up: |
| ... and [13 more](https://codecov.io/gh/pandas-dev/pandas/pull/18718/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18718?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/18718?src=pr&el=footer). Last update [1c1f507...68c0ff2](https://codecov.io/gh/pandas-dev/pandas/pull/18718?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. @jorisvandenbossche  @jorisvandenbossche 
Thank you for comments. PR updated. @jreback @jorisvandenbossche 
PR should be fully OK now. @stefansimik Yes, thanks!