Installation fails

```fish
❯ go version
go version go1.20.2 darwin/arm64
❯ go install github.com/apenwarr/git-subtrac
go: 'go install' requires a version when current directory is not in a module
Try 'go install github.com/apenwarr/git-subtrac@latest' to install the latest version
❯ go install github.com/apenwarr/git-subtrac@latest
go: github.com/apenwarr/git-subtrac@latest (in github.com/apenwarr/git-subtrac@v0.0.0-20200907023842-6f55d3a89654):
The go.mod file for the module providing named packages contains one or
more replace directives. It must not contain directives that would cause
it to be interpreted differently than if it were the main module.
❯ go get -v github.com/apenwarr/git-subtrac
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'.
```

I'm not familiar with Go, so I can't tell the problem resides in my environment or my project or `git-subtrac`, but seems like this software is only available for Go project?