##### 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 pcs[0][0] not in 'dl-?' or not frozenset(pcs[0][1:]).issubset('rwxstah-'):
                continue
            ztype = pcs[0][0]
            permstr = pcs[0][1:]
            version = pcs[1]
            ostype = pcs[2]
            size = int(pcs[3])
            path = to_text(pcs[7], errors='surrogate_or_strict')
            
            if path in self.excludes:
                out += 'Path %s is excluded on request\n' % path
                continue
            
            if path[-1] == '/':
                if ztype != 'd':
                    err += 'Path %s incorrectly tagged as "%s", but is a directory.\n' % (path, ztype)
                ftype = 'd'
            elif ztype == 'l':
                ftype = 'L'
            elif ztype == '-':
                ftype = 'f'
            elif ztype == '?':
                ftype = 'f'