- aspnet/AspNetCore-Internal#1649
- remove `$(StartArguments}` from project; conflicts with `--update`
- support v3 source _automatically_ when not using `--update`
- use NuGet's V3 source by default
- update README.md
nits:
- `--source` -> `--package-source` due to conflict with a `dotnet` argument
- address Markdown lint warnings in README.md
- grab a couple of improvements from 'release/2.2'
- never exit silently
- remove `first` special case