##### 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 -->

unarchive:
    src: /tmp/foo.zip
    dest: /usr/local/bin
    extra_opts:
    - --transform
    - s/^xxx/yyy/
'''
import binascii
import codecs
import datetime
import fnmatch
import grp
import os
import platform
import pwd
import re
import stat
import time
import traceback
from zipfile import ZipFile, BadZipfile
from ansible.module_utils.basic import AnsibleModule
from ansible.module_utils.urls import fetch_file
from ansible.module_utils._text import to_bytes, to_native, to_text
try:  
    from shlex import quote
except ImportError:  
    from pipes import quote
OWNER_DIFF_RE = re.compile(r': Uid differs$')
GROUP_DIFF_RE = re.compile(r': Gid differs$')
MODE_DIFF_RE = re.compile(r': Mode differs$')