##### 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 -->

if len(permstr) == 6:
                if path[-1] == '/':
                    permstr = 'rwxrwxrwx'
                elif permstr == 'rwx---':
                    permstr = 'rwxrwxrwx'
                else:
                    permstr = 'rw-rw-rw-'
                file_umask = umask
            elif 'bsd' in systemtype.lower():
                file_umask = umask
            else:
                file_umask = 0
            
            if len(permstr) != 9 or not ZIP_FILE_MODE_RE.match(permstr):
                raise UnarchiveError('ZIP info perm format incorrect, %s' % permstr)
            
            b_dest = os.path.join(self.b_dest, to_bytes(path, errors='surrogate_or_strict'))
            try:
                st = os.lstat(b_dest)
            except Exception:
                change = True
                self.includes.append(path)
                err += 'Path %s is missing\n' % path
                diff += '>%s++++++.?? %s\n' % (ftype, path)
                continue
            
            if ftype == 'd' and not stat.S_ISDIR(st.st_mode):
                change = True
                self.includes.append(path)