##### 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 -->

elif stat.S_ISREG(st.st_mode) and timestamp < st.st_mtime:
                        
                        out += 'File %s is newer, excluding file\n' % path
                        self.excludes.append(path)
                        continue
                else:
                    if timestamp != st.st_mtime:
                        change = True
                        self.includes.append(path)
                        err += 'File %s differs in mtime (%f vs %f)\n' % (path, timestamp, st.st_mtime)
                        itemized[4] = 't'
            
            if stat.S_ISREG(st.st_mode) and size != st.st_size:
                change = True
                err += 'File %s differs in size (%d vs %d)\n' % (path, size, st.st_size)
                itemized[3] = 's'
            
            if stat.S_ISREG(st.st_mode):
                crc = crc32(b_dest)
                if crc != self._crc32(path):
                    change = True
                    err += 'File %s differs in CRC32 checksum (0x%08x vs 0x%08x)\n' % (path, self._crc32(path), crc)
                    itemized[2] = 'c'
            
            
            if ftype != 'L':
                
                if self.file_args['mode']:
                    if isinstance(self.file_args['mode'], int):
                        mode = self.file_args['mode']