##### 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 -->

def __init__(self, src, b_dest, file_args, module):
        super(TarArchive, self).__init__(src, b_dest, file_args, module)
        
        self.zipflag = ''
class TarBzipArchive(TgzArchive):
    def __init__(self, src, b_dest, file_args, module):
        super(TarBzipArchive, self).__init__(src, b_dest, file_args, module)
        self.zipflag = '-j'
class TarXzArchive(TgzArchive):
    def __init__(self, src, b_dest, file_args, module):
        super(TarXzArchive, self).__init__(src, b_dest, file_args, module)
        self.zipflag = '-J'
def pick_handler(src, dest, file_args, module):
    handlers = [ZipArchive, TgzArchive, TarArchive, TarBzipArchive, TarXzArchive]
    reasons = set()
    for handler in handlers:
        obj = handler(src, dest, file_args, module)
        (can_handle, reason) = obj.can_handle_archive()
        if can_handle:
            return obj
        reasons.add(reason)
    reason_msg = ' '.join(reasons)
    module.fail_json(msg='Failed to find handler for "%s". Make sure the required command to extract the file is installed. %s' % (src, reason_msg))
def main():