##### 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 -->

MOD_TIME_DIFF_RE = re.compile(r': Mod time differs$')
EMPTY_FILE_RE = re.compile(r': : Warning: Cannot stat: No such file or directory$')
MISSING_FILE_RE = re.compile(r': Warning: Cannot stat: No such file or directory$')
ZIP_FILE_MODE_RE = re.compile(r'([r-][w-][SsTtx-]){3}')
INVALID_OWNER_RE = re.compile(r': Invalid owner')
INVALID_GROUP_RE = re.compile(r': Invalid group')
def crc32(path):
    ''' Return a CRC32 checksum of a file '''
    with open(path, 'rb') as f:
        file_content = f.read()
    return binascii.crc32(file_content) & 0xffffffff
def shell_escape(string):
    ''' Quote meta-characters in the args for the unix shell '''
    return re.sub(r'([^A-Za-z0-9_])', r'\\\1', string)
class UnarchiveError(Exception):
    pass
class ZipArchive(object):
    def __init__(self, src, b_dest, file_args, module):
        self.src = src
        self.b_dest = b_dest
        self.file_args = file_args
        self.opts = module.params['extra_opts']
        self.module = module
        self.excludes = module.params['exclude']
        self.includes = []
        self.cmd_path = self.module.get_bin_path('unzip')
        self.zipinfocmd_path = self.module.get_bin_path('zipinfo')
        self._files_in_archive = []
        self._infodict = dict()
    def _permstr_to_octal(self, modestr, umask):