Background: This is a follow-up to T320956. The purpose of this ticket is to add in the explainer text, since our first implementation for the release just has radio buttons for public/private without the explanations of what they mean.

As a campaign participant, I want to be able to choose between public or private registration on Special:RegisterForEvent, so that I can have the same options available to me as a non-JS user or a user who chooses to register via Special:RegisterForEvent for other reasons.

Special:RegisterForEvent is the no-JS experience for the registration experience. It can be accessed on the event page when the user right-clicks on the 'Register' button or if the user does not have JS enabled on their browser.

Example of a Special:RegisterForEvent page: https://meta.wikimedia.beta.wmflabs.org/wiki/Special:RegisterForEvent/1

Acceptance Criteria

• The "public registration" and "private registration" options in Special:RegisterForEvent should have labels explaining what "public" and "private" mean.

Visual example of Special:RegisterForEvent page (how it currently looks):

Visual example of how the page will be changed:

Note: this is not easy because OOUI does not support help text on individual radio options. The closest approach would be to use longer HTML labels, but it's unclear how accessible they'd be.