id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
679575175,MDU6SXNzdWU2Nzk1NzUxNzU=,4345,Improve Dataset documentation,14371165,closed,0,,,9,2020-08-15T13:27:33Z,2020-10-27T19:47:51Z,2020-10-27T19:47:51Z,MEMBER,,,,"**Is your feature request related to a problem? Please describe.**
As a new user I find it difficult to get a new dataset initialized because the necessary parameters are not shown in the docstring. 
I have to google ""xarray dataset"" to get to http://xarray.pydata.org/en/stable/generated/xarray.Dataset.html to figure it out.

In the figure below xarray.Dataset does not show the necessary parameters in the help pane:
![image](https://user-images.githubusercontent.com/14371165/90313058-aab66000-df09-11ea-9f3a-d2d3f2698b66.png)

Compare to pandas.DataFrame that includes it:
![image](https://user-images.githubusercontent.com/14371165/90313083-e94c1a80-df09-11ea-8013-a7ffe90ab4d8.png)

**Describe the solution you'd like**
Looking at https://github.com/pydata/xarray/blob/master/xarray/core/dataset.py#L428 the `xr.Dataset.__init__.__doc__` does contain the necessary parameters so the suggestion is to simply move or copy that information up one level to` xr.Dataset.__doc__`

For reference pandas does not use a docstring for the __init__ method:
https://github.com/pandas-dev/pandas/blob/v1.1.0/pandas/core/frame.py#L339-L9257

The pandas docs also includes a few simple copy/pasteable examples on how to initialize. So a xarray example would be:
```python
>>> import numpy as np
>>> import xarray as xr
>>> x = np.arange(4)
>>> y = 2*x
>>> ds = xr.Dataset({'y': (['x'], y)},
...                 coords={'x': x})
>>> print(ds)
<xarray.Dataset>
Dimensions:  (x: 4)
Coordinates:
  * x        (x) int32 0 1 2 3
Data variables:
    y        (x) int32 0 2 4 6
```
Or take some examples from http://xarray.pydata.org/en/stable/quick-overview.html#datasets or http://xarray.pydata.org/en/stable/data-structures.html#dataset although I found those  a little bit confusing as they were dependent on previous results or rather complex with many dimensions.

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.7 (default, May  6 2020, 11:45:54) [MSC v.1916 64 bit (AMD64)]
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 58 Stepping 9, GenuineIntel
byteorder: little
LC_ALL: None
LANG: en
LOCALE: None.None
libhdf5: 1.10.4
libnetcdf: None

xarray: 0.15.0
pandas: 1.0.3
numpy: 1.18.1
scipy: 1.4.1
netCDF4: None
pydap: None
h5netcdf: None
h5py: 2.10.0
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2.14.0
distributed: 2.22.0
matplotlib: 3.1.3
cartopy: None
seaborn: 0.10.0
numbagg: None
setuptools: 49.2.1.post20200807
pip: 20.2.1
conda: 4.8.3
pytest: 6.0.1
IPython: 7.17.0
sphinx: 3.2.0
C:\ProgramData\Anaconda3\lib\site-packages\setuptools\distutils_patch.py:26: UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least import Setuptools first.
  ""Distutils was imported before Setuptools. This usage is discouraged ""

</details>
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