Rhino3dmIO is already available via nuget – both v6 and v7 packages. These packages are Windows and Mac only.
Recently, @stevebaer updated the rhino3dm project to include the .NET code required to compile rhino3dm.net yourself. If you want to use the rhino3dm library in a .NET project on Linux, then this is currently the only way.
rhino3dm.net is just a rebranding of Rhino3dmIO, since we now also have JavaScript and Python versions of the library and it does more than just IO!