Findable, tutorial-style docs for "how to add custom fields"

Currently there are reference docs for the IDatasetForm plugin interface and there's a working example in ckanext/example_idatasetform but there are no nice, easy-to-find, tutorial-style docs for "how to add custom fields". This wiki page has been contributed recently:

<https://github.com/okfn/ckan/wiki/How-to-Add-Custom-Fields-to-CKAN-2.0>

It's a start and something like this should be integrated into the official docs.