Update MFA page

[sherbang]

Looks like the MFA issue was pushed to a later milestone. Update the documentation to point to the issue instead of the milestone.

Checklist

• [X ] I have read the contributing guidelines.
• [X ] I have read the security policy.
• [X ] I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• [X ] I have added or changed the documentation.

Further comments

[CLAassistant]

All committers have signed the CLA.

[aeneasr]

Thank you!