##### SUMMARY
The unarchive module is missing documentation on its return values.
Only the `list_files` option mentions it at all:
> If set to True, return the list of files that are contained in the tarball.

It does not mention how this list is returned (Spoiler: It's in the `files` key, as a list of file names).
A `RETURN` section should be added to the module documentation.
Ideally, the `EXAMPLES` section should be extended to include one or two examples that use the return values somehow.

##### ISSUE TYPE
- Documentation Report

##### COMPONENT NAME
modules/files/unarchive.py

##### ANSIBLE VERSION

```
ansible 2.9.2
  config file = None
  configured module search path = ['/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib64/python3.6/site-packages/ansible
  executable location = /usr/lib/python-exec/python3.6/ansible
  python version = 3.6.9 (default, Oct  5 2019, 11:39:46) [GCC 8.3.0]
```

##### CONFIGURATION
not relevant

##### OS / ENVIRONMENT
not relevant

##### ADDITIONAL INFORMATION
<!--- Describe how this improves the documentation, e.g. before/after situation or screenshots -->

<!--- HINT: You can paste gist.github.com links for larger files -->

cmd = [self.cmd_path, '-o']
        if self.opts:
            cmd.extend(self.opts)
        cmd.append(self.src)
        
        
        
        
        if self.excludes:
            cmd.extend(['-x'] + self.excludes)
        cmd.extend(['-d', self.b_dest])
        rc, out, err = self.module.run_command(cmd)
        return dict(cmd=cmd, rc=rc, out=out, err=err)
    def can_handle_archive(self):
        if not self.cmd_path:
            return False, 'Command "unzip" not found.'
        cmd = [self.cmd_path, '-l', self.src]
        rc, out, err = self.module.run_command(cmd)
        if rc == 0:
            return True, None
        return False, 'Command "%s" could not handle archive.' % self.cmd_path
class TgzArchive(object):