Add an example of how to modify an existing version of the HDF5 database

[wtbarnes]

This is useful if you have, for example, an updated model for a specific ion. This is most easily done if you have information already in the CHIANTI file format.

As an example, this dataset provides an updated model of Fe XVI for calculating the satellite lines of Fe XVII: https://zenodo.org/records/11474529.

[wtbarnes]

Here's an example of how to do that:

for file in fe16_files:
    p = fiasco.io.Parser(file)
    table = p.parse()
    with h5py.File('/Users/wtbarnes/Desktop/chianti_v10.1.0_modified_fe16.h5', mode='a') as hf:
        if (dset_name:=f'{p.element}/{p.ion_name}/{p.filetype}') in hf:
            del hf[dset_name]
        p.to_hdf5(hf, table)