Docs: Incorrect prefix for custom fields

[smarts]

In the docs it states the prefix for Additional Fill-in Fields as KPH: instead of KPH: (space at the end).
It took a while before I landed at another resource which had the correct prefix. I attempted to fix the docs myself in a fork, but either the adoc spec itself does not like the trailing space or github's adoc parser doesn't like it. When I made the change it showed up as
`KPH: `
instead of
KPH: .

I assume this is a problem with the docs as opposed to a bug, but I'll let y'all decide 🙂