Document forced MFA page

[mooreds]

As of 1.42, you can force users to enable MFA. This can be done at the tenant or application level (latter requires the Enterprise plan).

We don't document how that looks to the end user.

The right place is probably https://fusionauth.io/docs/v1/tech/guides/multi-factor-authentication#forcing-mfa

I think adding an image or two would be fine and clarifying that the user will have a chance to add an MFA method on first login to an application or tenant which requires MFA.