[Neuroimaging] Discourse discussions ported to Github Discussions

[Matthew Brett]

Hi,

Sorry for the inconvenience, but Discourse has very reasonably closed
down our nipy.discourse.group site because we were not using it.

Rather than re-open the site, I've moved all the content to Github
discussions.  So, you'll find all previous discussion of:

* Neuroimaging data formats at
https://github.com/orgs/open-dicom/discussions/categories/neuroimaging-data-formats
* DICOM conversion at
https://github.com/orgs/open-dicom/discussions/categories/dicom
* Surface API at https://github.com/orgs/nipy/discussions/categories/surface-api

This also means that I've enabled Github discussions for the Nipy
organization, and the Open-DICOM organization.

If you spot anything missing or incorrect - please either edit, or let me know.

Cheers,

Matthew