Clarity in documentation and code around chunksizes

1. If you search the document for chunksizes you get a lot of stuff about dask chunk sizes first. Can be confusing if you are interested in variable chunksizes.

2. The method v.data.set_nc_hdf5_chunksizes actually sets the chunk shape, not the volume/size.

E.g. the word size is clearly about the volume, as can be seen from the documentation:

https://docs.unidata.ucar.edu/nug/current/netcdf_perf_chunking.html says "Currently the netCDF default chunk size is 4MiB The current default chunking strategy of the netCDF library is to balance access time alongany of a variable's dimensions, by using chunk shapes similar to the shape of the entire variable but small enough that the resulting chunk size is less than or equal to the default chunk size."

Beginne damit, in der Dokumentation und im Code nach “chunksizes” zu suchen und v.data.set_nc_hdf5_chunksizes zu untersuchen. Vergleiche die Verweise auf Dask-Chunk-Größen mit den Chunk-Formen und -Größen von Variablen. Als erledigt gilt die Aufgabe, wenn die Terminologie und die Dokumentation diese Konzepte klar unterscheiden und genau beschreiben, was die Methode festlegt.