Problem
The default account creation flow uses a captcha to ensure a human user, but captchas have well-known accessibility problems. For this reason, the wikis provide alternative account creation methods. We should allow the user to access them.
See the equivalent iOS ticket: T154728
Proposed solution
As per the iOS app, add a link to the alternative account creation site on the CAPTCHA screen:
Tapping on the "Request an account" opens the "Wikipedia: Request an account" page at https://en.wikipedia.org/wiki/Wikipedia:Request_an_account