include details on Enketo styles

I searched on docs.getodk.org and xlsform.org and couldn't find the equivalent of this info from the Kobo docs on [Using Alternative Enketo Web Form Styles](https://support.kobotoolbox.org/alternative_enketo.html).

Is this info included somewhere that I missed? Was it intentionally left out? Should it be added?

Start by comparing the linked Kobo page with searches on docs.getodk.org and xlsform.org for alternative Enketo styles. Determine whether the information is already documented or intentionally omitted, then document the relevant details if the project decides they belong in the ODK docs.

Written by the indexing model from the issue text.