Migrate volunteer section into separate file

[akhepcat]

This moves the volunteer list out of the main readme into a separate file.

This is being done in order to simplify future updates of the volunteer list without impacting the readme.

[philcrump]

If we added a "geographical area" description to https://galmon.eu/observers.html (could be calculated from the rough lat/lon, or freeform as per operator/remark), then this (already outdated) list becomes redundant.

[akhepcat]

If we added a "geographical area" description to https://galmon.eu/observers.html (could be calculated from the rough lat/lon, or freeform as per operator/remark), then this (already outdated) list becomes redundant.

True enough - this file, until that point, could also be a place to list "wanted areas" and it does help to keep the front-page clutter down.
I also thought about moving it to wiki space, but that can't be done via a PR as far as i know.

[philcrump]

A "wanted areas" list does sound good, actively encouraging those who see their area listed, rather than actively discouraging those whose area is already covered like the current list does.

I also agree that this file should be separated from the software versioning. The github project wiki would make sense as a place to start collecting this, and other guides and howto information. I think @ahupowerdns needs to enable access to it somehow.