DOC: improve groupby.DataFrameGroupBy.resample docstring
After asking for feedback, this is the very minimal _docstring_ that we interpret that would be acceptable. 

This is in order to unlock the full list of functions we have assigned for the pandas documentation sprint.

If there is something to be improved here please tell us. Also we may make a new push of this documentation including the full scope of the _args_ and _kwargs_ parameters and more examples.
Hello @pandres! Thanks for updating the PR.



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

##### Comment last updated on March 09, 2018 at 16:01 Hours UTC Ah, OK, I see you actually copied the examples from the Series/DataFrame.resample docstring, that's why they were off topic :) 
(but, best to only open a PR when you actually have changes, work in progress is certainly fine, but best that they are already relevant)
 @jorisvandenbossche, thank you for the feedback. Maybe I rushed here, we were just doing a warm-up for the sprint on Saturday. 

We do have questions though, related with the `Series` and `DataFrames` examples. I'll check your comment in https://github.com/pandas-dev/pandas/pull/20020#discussion_r172646215 If something is unclear, I think it is best to ask on the gitter channel # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20020?src=pr&el=h1) Report
> Merging [#20020](https://codecov.io/gh/pandas-dev/pandas/pull/20020?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e02f73787bfbd00ce2ad899542538dfad854eb01?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/20020/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20020?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20020      +/-   ##
==========================================
+ Coverage   91.67%   91.67%   +<.01%     
==========================================
  Files         150      150              
  Lines       49096    49096              
==========================================
+ Hits        45007    45009       +2     
+ Misses       4089     4087       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.05% <ø> (ø)` | :arrow_up: |
| #single | `41.87% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20020?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/20020/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `92.14% <ø> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20020/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `83.85% <0%> (+0.2%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20020?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/20020?src=pr&el=footer). Last update [e02f737...d9331ff](https://codecov.io/gh/pandas-dev/pandas/pull/20020?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Not sure what's going on with the circleci failures.