##### 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 -->

try:
            run_owner = pwd.getpwuid(run_uid).pw_name
        except (TypeError, KeyError):
            run_owner = run_uid
        try:
            run_group = grp.getgrgid(run_gid).gr_name
        except (KeyError, ValueError, OverflowError):
            run_group = run_gid
        
        fut_owner = fut_uid = None
        if self.file_args['owner']:
            try:
                tpw = pwd.getpwnam(self.file_args['owner'])
            except KeyError:
                try:
                    tpw = pwd.getpwuid(int(self.file_args['owner']))
                except (TypeError, KeyError, ValueError):
                    tpw = pwd.getpwuid(run_uid)
            fut_owner = tpw.pw_name
            fut_uid = tpw.pw_uid
        else:
            try:
                fut_owner = run_owner
            except Exception:
                pass
            fut_uid = run_uid
        
        fut_group = fut_gid = None
        if self.file_args['group']:
            try: