Add NcML previewer to gdcc repo

[pdurbin]

I'm using this to track gdcc/dataverse-previewers#17 where I'm trying to add a previewer for NcML files that are generated by Dataverse with code in this PR:

• extract metadata (NcML XML) from NetCDF/HDF5 files, new "requirements" option for external tools #9239

[pdurbin]

The PR I submitted has been merged:

• add NcML previewer #17 gdcc/dataverse-previewers#18

So I'll close this issue.