Document twofactor_backup_codes app

[karakayasemi]

What Needs to be Documented?

Document the usage and purpose of twofactor_backup_codes app. https://marketplace.owncloud.com/apps/twofactor_backup_codes

Where Does This Need To Be Documented?

• Admin Manual We may consider to open a chapter for 2FA providers.

What Type Of Content Change Is This? (Optional)

• [x] New Content Addition

Which Manual Does This Relate To? (Optional)

• [x] Admin Manual