I wanted to install a package form a git repo. So I created my own package
manifest and did `guix package -m package.scm`. It fetched all dependencies but
then I got this error:

```
guix build: error: while setting up the build environment: getting attributes
of path `/etc/services': No such file or directory
```

I could solve it after `touch /etc/services`. Not sure why guix needs this at
all (it has not written anything on the file). But it needs it, so I suggest
the file is created in the package installation.

Thanks.