Improve docs for paket config add-token

DOcs for paket config add-token are cryptic

Spent 30 mins trying to guess what tag means, while trying to provide my nuget apikey

Repro steps

I am using paket thus
$ .paket/paket.exe push file bin/fss_postgres.1.4.0.nupkg
Paket version 3.7.3.0
Paket failed with:
Could not push package bin/fss_postgres.1.4.0.nupkg due to missing credentials for the url https://nuget.org/api/v2/package. Please specify a NuGet API key via the command line, the environment variable "nugetkey", or by using 'paket config add-token'.

Docs for add-token
https://fsprojects.github.io/Paket/commands/config.html

say you use it with TAG and TOKEN. What is the TAG? I tried nuget nugetapikey the nuget URL etc, and unclear what TAG should be.

Expected behavior

Would be nice if docs contained an example (with a fake API key) that works for nuget

Start with the config add-token section at https://fsprojects.github.io/Paket/commands/config.html and compare it with the reported paket config add-token and NuGet push commands. Add a working example using a fake NuGet API key, clarify what TAG represents, and verify the rendered documentation explains the credentials setup.