##### 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 -->

- Specify additional options by passing in an array.
      - Each space-separated command-line option should be a new element of the array. See examples.
      - Command-line options with multiple elements must use multiple lines in the array, one for each element.
    type: list
    elements: str
    default: ""
    version_added: "2.1"
  remote_src:
    description:
      - Set to C(yes) to indicate the archived file is already on the remote system and not local to the Ansible controller.
      - This option is mutually exclusive with C(copy).
    type: bool
    default: no
    version_added: "2.2"
  validate_certs:
    description:
      - This only applies if using a https URL as the source of the file.
      - This should only set to C(no) used on personally controlled sites using self-signed certificate.
      - Prior to 2.2 the code worked as if this was set to C(yes).
    type: bool
    default: yes
    version_added: "2.2"
extends_documentation_fragment:
- decrypt
- files
todo:
    - Re-implement tar support using native tarfile module.
    - Re-implement zip support using native zipfile module.
notes:
    - Requires C(zipinfo) and C(gtar)/C(unzip) command on target host.