Replace(?) deprecated installation instructions in "Instrumenting a Go application for Prometheus" docs

[atimeofday]

Hello,

As a new user of both Go and Prometheus, I ran into some issues and tentatively believe the instructions for installing the prometheus/client_golang libraries are outdated as of Go 1.17 in... August 2021. It appears go get was deprecated outside of Go Modules, and requires the creation of a Go Module first. Please let me know if this impression is incorrect, or if a small PR to adjust the instructions might be welcome.

Issue location: https://github.com/prometheus/docs/blob/main/content/docs/guides/go-application.md#installation
Issue contents:

go get github.com/prometheus/client_golang/prometheus
go get github.com/prometheus/client_golang/prometheus/promauto
go get github.com/prometheus/client_golang/prometheus/promhttp

Potential solution: preface go get instructions with go mod init <module_name> and a link to Go Module documentation

[beorn7]

I guess you are right, these are outdated instruction to get Go packages. A PR fixing this would be very welcome.

[lhajouji]

Hello @beorn7,

I would gladly work on this.
Would you please assign it to me ?

Thanks !