##### 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 -->

else:
                        try:
                            mode = int(self.file_args['mode'], 8)
                        except Exception as e:
                            try:
                                mode = AnsibleModule._symbolic_mode_to_octal(st, self.file_args['mode'])
                            except ValueError as e:
                                self.module.fail_json(path=path, msg="%s" % to_native(e), exception=traceback.format_exc())
                
                elif ztype == '?':
                    mode = self._permstr_to_octal(permstr, 0)
                else:
                    mode = self._permstr_to_octal(permstr, file_umask)
                if mode != stat.S_IMODE(st.st_mode):
                    change = True
                    itemized[5] = 'p'
                    err += 'Path %s differs in permissions (%o vs %o)\n' % (path, mode, stat.S_IMODE(st.st_mode))
            
            owner = uid = None
            try:
                owner = pwd.getpwuid(st.st_uid).pw_name
            except (TypeError, KeyError):
                uid = st.st_uid
            
            if run_uid != 0 and (fut_owner != run_owner or fut_uid != run_uid):
                raise UnarchiveError('Cannot change ownership of %s to %s, as user %s' % (path, fut_owner, run_owner))
            if owner and owner != fut_owner:
                change = True
                err += 'Path %s is owned by user %s, not by user %s as expected\n' % (path, owner, fut_owner)
                itemized[6] = 'o'