should use both `doc` and `label` when generating CLI for a CWL description

Currently only `doc` is used

https://github.com/common-workflow-language/cwltool/blob/9a4b7b1f3e585cce026c07798df5c82b7fa213e0/cwltool/main.py#L402
https://github.com/common-workflow-language/cwltool/blob/9a4b7b1f3e585cce026c07798df5c82b7fa213e0/cwltool/main.py#L360