##### 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 -->

from __future__ import absolute_import, division, print_function
__metaclass__ = type
DOCUMENTATION = r'''
---
module: unarchive
version_added: '1.4'
short_description: Unpacks an archive after (optionally) copying it from the local machine.
description:
     - The C(unarchive) module unpacks an archive. It will not unpack a compressed file that does not contain an archive.
     - By default, it will copy the source file from the local system to the target before unpacking.
     - Set C(remote_src=yes) to unpack an archive which already exists on the target.
     - If checksum validation is desired, use M(ansible.builtin.get_url) or M(ansible.builtin.uri) instead to fetch the file and set C(remote_src=yes).
     - For Windows targets, use the M(community.windows.win_unzip) module instead.
options:
  src:
    description:
      - If C(remote_src=no) (default), local path to archive file to copy to the target server; can be absolute or relative. If C(remote_src=yes), path on the
        target server to existing archive file to unpack.
      - If C(remote_src=yes) and C(src) contains C(://), the remote machine will download the file from the URL first. (version_added 2.0). This is only for
        simple cases, for full download support use the M(ansible.builtin.get_url) module.
    type: path
    required: true
  dest:
    description:
      - Remote absolute path where the archive should be unpacked.
    type: path
    required: true
  copy:
    description: