Once you’ve followed the (somewhat annoying) install steps to get .Net core installed and the apt repo setup from https://www.microsoft.com/net/core, you can just do this:
sudo apt install nuget
and you’ll have a working nuget on your local machine:
$ cat /etc/issue
Ubuntu 16.04.1 LTS \n \l
$ nuget
NuGet Version: 2.8.7.0
usage: NuGet <command> [args] [options]
Type 'NuGet help <command>' for help on a specific command.
Notice that as of the time of writing do not run nuget update -self, as although it will successfully install a more recent version of nuget, that version won’t actually run.
If you do break it though, you can always just blow it away and reinstall:
sudo apt remove nuget
sudo apt install nuget