##### 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 -->

remote_src = module.params['remote_src']
    file_args = module.load_file_common_arguments(module.params)
    
    if not os.path.exists(src):
        if not remote_src:
            module.fail_json(msg="Source '%s' failed to transfer" % src)
        
        elif '://' in src:
            src = fetch_file(module, src)
        else:
            module.fail_json(msg="Source '%s' does not exist" % src)
    if not os.access(src, os.R_OK):
        module.fail_json(msg="Source '%s' not readable" % src)
    
    try:
        if os.path.getsize(src) == 0:
            module.fail_json(msg="Invalid archive '%s', the file is 0 bytes" % src)
    except Exception as e:
        module.fail_json(msg="Source '%s' not readable, %s" % (src, to_native(e)))
    
    if not os.path.isdir(b_dest):
        module.fail_json(msg="Destination '%s' is not a directory" % dest)
    handler = pick_handler(src, b_dest, file_args, module)
    res_args = dict(handler=handler.__class__.__name__, dest=dest, src=src)
    
    check_results = handler.is_unarchived()
    
    
    if module.check_mode:
        res_args['changed'] = not check_results['unarchived']