##### 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 true, the file is copied from local controller to the managed (remote) node, otherwise, the plugin will look for src archive on the managed machine.
      - This option has been deprecated in favor of C(remote_src).
      - This option is mutually exclusive with C(remote_src).
    type: bool
    default: yes
  creates:
    description:
      - If the specified absolute path (file or directory) already exists, this step will B(not) be run.
    type: path
    version_added: "1.6"
  list_files:
    description:
      - If set to True, return the list of files that are contained in the tarball.
    type: bool
    default: no
    version_added: "2.0"
  exclude:
    description:
      - List the directory and file entries that you would like to exclude from the unarchive action.
    type: list
    elements: str
    version_added: "2.1"
  keep_newer:
    description:
      - Do not replace existing files that are newer than files from the archive.
    type: bool
    default: no
    version_added: "2.1"
  extra_opts:
    description: