improve documentation

We should improve the documentation for all the group arguments, field types and filters that are included in the plugin. This should probably live in the wiki here on Github instead of the growing readme.

The issue identifies the plugin's group arguments, field types, and filters, and proposes moving their documentation from the growing README to the GitHub wiki. Start by reviewing the existing README and plugin documentation, then inventory the documented and undocumented items. Done means the relevant arguments, types, and filters are covered in the wiki without leaving the README as the only reference.

Written by the indexing model from the issue text.