Docs for updating default mapping is incorrect

[ewohnlich]

I want to change the default mapping so that SearchableText provides both a raw keyword field and text field with snowball analyzer for a project. The docs https://github.com/collective/collective.elasticsearch/blob/master/docs/config.rst suggest I can create my own adapter and apply a layer. However, this appears to be invalid ZCML - adapters can't have layers

zope.configuration.exceptions.ConfigurationError: ('Unrecognized parameters:', 'layer')

Assuming I am correct here, I don't think there's currently a better way to update these than monkey patching? I've also monkey patched the create_mapping for collective.elasticsearch.indexes.EZCTextIndex but this appears to not apply for those fields in the _default_mapping.