Use `ncks` to reproduce example value(s)

# Summary

Just a quick issue to memoize efforts by @dholstius.

# Details

From the [README]:

> For example, if you wanted to extract the 0th layer of the ISRM's SO4 values:
```
>> ncks -v pSO4 -d layer,0 big_isrm.ncf pSO4L0.nc
```

## Slicing `isrm_v1.2.1.ncf`

I'm running into this on my MacBook:

```
$ ncwa isrm_v1.2.1.ncf test.nc
ERROR: nco__open() unable to open file "isrm_v1.2.1.ncf"
ERROR NC_EVARSIZE One or more variable sizes violate format constraints
```

... and the following:

```
HINT: NC_EVARSIZE errors occur when attempting to copy or aggregate input files together into an output file that exceeds the per-file capacity of the output file format, and when trying to copy, aggregate, or define individual variables that exceed the per-variable constraints of the output file format. The per-file limit of all netCDF formats is not less than 8 EiB on modern computers, so any NC_EVARSIZE error is almost certainly due to violating a per-variable limit. Relevant limits: netCDF3 NETCDF_CLASSIC format limits fixed variables to sizes smaller than 2^31 B = 2 GiB ~ 2.1 GB, and record variables to that size per record. A single variable may exceed this limit if and only if it is the last defined variable. netCDF3 NETCDF_64BIT_OFFSET format limits fixed variables to sizes smaller than 2^32 B = 4 GiB ~ 4.2 GB, and record variables to that size per record. Any number of variables may reach, though not exceed, this size for fixed variables, or this size per record for record variables. The netCDF3 NETCDF_64BIT_DATA and netCDF4 NETCDF4 formats have no variable size limitations of real-world import. If any variable in your dataset exceeds these limits, alter the output file to a format capacious enough, either netCDF3 classic with 64-bit offsets (with -6 or --64), to PnetCDF/CDF5 with 64-bit data (with -5), or to netCDF4 (with -4 or -7). For more details, see http://nco.sf.net/nco.html#fl_fmt
```

I've tried various `–fl_fmt` flags, but no avail. Even trying to just dump the format throws the same error:

```
$ ncdump -k isrm_v1.2.1.ncf
ncdump: isrm_v1.2.1.ncf: NetCDF: One or more variable sizes violate format constraints
```

## Related Issues

- #8

[README]: ../blob/master/References/Handoff/ISRM%20readme.md

Start with References/Handoff/ISRM readme.md and the README command using ncks, then run ncdump -k isrm_v1.2.1.ncf to reproduce the reported failure. Review related issue #8 and the ncwa, ncks, and ncdump outputs. Done means documenting a reproducible way to inspect or extract the pSO4 layer values, or clearly recording why the example cannot be reproduced.

Written by the indexing model from the issue text.