##### 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 -->

elif check_results['unarchived']:
        res_args['changed'] = False
    else:
        
        try:
            res_args['extract_results'] = handler.unarchive()
            if res_args['extract_results']['rc'] != 0:
                module.fail_json(msg="failed to unpack %s to %s" % (src, dest), **res_args)
        except IOError:
            module.fail_json(msg="failed to unpack %s to %s" % (src, dest), **res_args)
        else:
            res_args['changed'] = True
    
    if check_results.get('diff', False):
        res_args['diff'] = {'prepared': check_results['diff']}
    
    if res_args.get('diff', True) and not module.check_mode:
        
        for filename in handler.files_in_archive:
            file_args['path'] = os.path.join(b_dest, to_bytes(filename, errors='surrogate_or_strict'))
            try:
                res_args['changed'] = module.set_fs_attributes_if_different(file_args, res_args['changed'], expand=False)
            except (IOError, OSError) as e:
                module.fail_json(msg="Unexpected error when accessing exploded file: %s" % to_native(e), **res_args)
    if module.params['list_files']:
        res_args['files'] = handler.files_in_archive
    module.exit_json(**res_args)
if __name__ == '__main__':
    main()