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
575939446,MDU6SXNzdWU1NzU5Mzk0NDY=,3830,"Documentation request: add examples for carrying out ""ncecat"" in xarray",19657652,open,0,,,4,2020-03-05T01:58:17Z,2023-04-13T20:06:20Z,,NONE,,,,"<!-- A short summary of the issue, if appropriate -->

In climate science, a very common task involves concatenating NetCDF files with identical variables, dimensions, and coordinates along a brand new ""ensemble member"" or ""record"" dimension. With the NetCDF Operators, this is accomplished using [`ncecat`](http://nco.sourceforge.net/nco.html#ncecat-netCDF-Ensemble-Concatenator
). 

#### MCVE Code Sample

Currently, it seems the correct way to do this in xarray is with [`xarray.combine_nested`](http://xarray.pydata.org/en/stable/generated/xarray.combine_nested.html) as follows:

```python
import xarray as xr
files = ['member1.nc', 'member2.nc', ...]
ds = xr.open_mfdataset(
    files,
    combine='nested',
    concat_dim='record',
)
```

#### Problem Description

While this works, there does not seem to be any mention of this use case in the [`combine_nested`](http://xarray.pydata.org/en/stable/generated/xarray.combine_nested.html) or [`open_mfdataset`](http://xarray.pydata.org/en/stable/generated/xarray.open_mfdataset.html) docs... and using `combine='nested'` to concatenate along a brand new dimension feels quite unintuitive to me.

It would be nice to have examples in `combine_nested` and/or `open_mfdataset` with this special usage or mention the possibility of creating *brand new* dimensions with `concat_dim`. For example:

```python
In [1]: import xarray as xr 
   ...: datasets = [
   ...:     xr.Dataset({'temp': (('x', 'y'), np.random.rand(10, 20))})
   ...:     for i in range(3)
   ...: ]
   ...: xr.combine_nested(datasets, concat_dim='record')
Out[1]:
<xarray.Dataset>
Dimensions:  (record: 3, x: 10, y: 20)
Dimensions without coordinates: record, x, y
Data variables:
    temp     (record, x, y) float64 0.32 0.4897 0.2659 ... 0.3485 0.0251 0.399
```

#### Output of ``xr.show_versions()``

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