Update Readme for newer Go versions

[bjornaer]

Please read CONTRIBUTING.md

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Version: v0.5.0
Installation method: Go

Golang now enables installing via go install <package>@<version>(which gets and builds) and does not allow go get outside of go modules anymore, so on the install section of the readme it would be nice to have that change reflected!

[bjornasm]

Came here to file this issue, had a double take when I read your nick @bjornaer

[bjornaer]

Came here to file this issue, had a double take when I read your nick @bjornaer

I got confused by the GitHub notification too haha