Update quickstart.md

[ejether]

go get is no longer supported outside of a module.

✗ go version
go version go1.20.3 darwin/arm64

▶  go get github.com/fairwindsops/nova
go: go.mod file not found in current directory or any parent directory.
	'go get' is no longer supported outside a module.
	To build and install a command, use 'go install' with a version,
	like 'go install example.com/cmd@latest'
	For more information, see https://golang.org/doc/go-get-install-deprecation
	or run 'go help get' or 'go help install'.

✗ go install github.com/fairwindsops/nova
go: 'go install' requires a version when current directory is not in a module
	Try 'go install github.com/fairwindsops/nova@latest' to install the latest version

This PR fixes #

Out dated documentation for new go standards

Checklist

• I have signed the CLA
• I have updated/added any relevant documentation

Description

What's the goal of this PR?

What changes did you make?

What alternative solution should we consider, if any?

[CLAassistant]

All committers have signed the CLA.

[ejether]

I noticed a couple other references to go get that I didn't catch in this.

[rbren]

Thanks EJ!