##### 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 -->

tgr = grp.getgrnam(self.file_args['group'])
            except (ValueError, KeyError):
                try:
                    
                    
                    tgr = grp.getgrgid(int(self.file_args['group']))
                except (KeyError, ValueError, OverflowError):
                    tgr = grp.getgrgid(run_gid)
            fut_group = tgr.gr_name
            fut_gid = tgr.gr_gid
        else:
            try:
                fut_group = run_group
            except Exception:
                pass
            fut_gid = run_gid
        for line in old_out.splitlines():
            change = False
            pcs = line.split(None, 7)
            if len(pcs) != 8:
                
                continue
            
            if len(pcs[0]) != 7 and len(pcs[0]) != 10:
                continue
            if len(pcs[6]) != 15:
                continue