##### 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 -->

unarchived = True
        old_out = out
        out = ''
        run_uid = os.getuid()
        
        
        
        for line in old_out.splitlines() + err.splitlines():
            
            
            if EMPTY_FILE_RE.search(line):
                continue
            if run_uid == 0 and not self.file_args['owner'] and OWNER_DIFF_RE.search(line):
                out += line + '\n'
            if run_uid == 0 and not self.file_args['group'] and GROUP_DIFF_RE.search(line):
                out += line + '\n'
            if not self.file_args['mode'] and MODE_DIFF_RE.search(line):
                out += line + '\n'
            if MOD_TIME_DIFF_RE.search(line):
                out += line + '\n'
            if MISSING_FILE_RE.search(line):
                out += line + '\n'
            if INVALID_OWNER_RE.search(line):
                out += line + '\n'
            if INVALID_GROUP_RE.search(line):
                out += line + '\n'
        if out:
            unarchived = False
        return dict(unarchived=unarchived, rc=rc, out=out, err=err, cmd=cmd)
    def unarchive(self):