Add documentation for licenses.yaml and remove module attribute if not needed

For more info, see https://github.com/apache/druid/pull/8992#discussion_r396128681

Start by locating licenses.yaml and read the discussion in pull request 8992 linked by the issue. Determine what documentation is missing and whether the module attribute is needed; done means the file is documented and the attribute is removed only if the discussion supports that change.

Written by the indexing model from the issue text.