Mixin rendering instructions fail with go v1.18

[adeverteuil]

I tried installing mixtool with go v1.18 and I got an error. It works fine with go v1.17.8 but then I get a deprecation notice.

With go v1.18:

$ GO111MODULE=on go get github.com/monitoring-mixins/mixtool/cmd/mixtool
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'.

With go v1.17:

$ GO111MODULE=on go get github.com/monitoring-mixins/mixtool/cmd/mixtool
go get: installing executables with 'go get' in module mode is deprecated.
        Use 'go install pkg@version' instead.
        For more information, see https://golang.org/doc/go-get-install-deprecation
        or run 'go help get' or 'go help install'.