Installation instructions

Hey, I'm new to Go and having some difficulties compiling the project.

When running 

```sh
go build ./main.go
```

I get the following message:

```
main.go:11:2: no required module provides package github.com/xigh/go-wavreader: go.mod file not found in current directory or any parent directory; see 'go help modules'
```

Please help :)