Example of writing a dataset

### What are you trying to do?
I'm trying to write an array in a dataset, what I do is reading it, applying some operations to the data and then I want to write it back. At the moment of writing it back I've tried:

```
dataToWrite := ts.Data().([]float32)
err = ds.WriteSubset(dataToWrite, nil, nil)
```

```
dataToWrite := ts.Data().([]float32)
err = ds.WriteSubset(&dataToWrite, nil, nil)
```

```
dataToWrite := ts.Data().([]float32)
err = ds.WriteSubset(dataToWrite, dspace, nil)
```

etc...

but all of them fail with either:

```
panic: reflect.Value.UnsafeAddr of unaddressable value
```

or

```
panic: code -1
```

so I'm not sure what I'm missing here

thanks in advance

Start by reproducing the reported calls to ts.Data() and ds.WriteSubset(), including slice, pointer, and dspace arguments. Read the WriteSubset usage and dataset-writing examples available in the repository, then document a working array-writing example and the expected handling of these arguments.

Written by the indexing model from the issue text.