Added comment

docs/tfa.md

@@ -2,6 +2,7 @@ So far three methods for *Two Factor Authentication* are implemented: U2F, Yubi
 
 - For U2F to work, you need an encrypted connection to the server (HTTPS) as well as a FIDO security key.
 - Both U2F and Yubi OTP work well with the fantastic [Yubikey](https://www.yubico.com).
+<!-- @andryyy, ich bin mir nicht sicher, was du mit diesem Absatz sagen möchtest, Yubi OTP oder U2F? -->
 - While Yubi OTP needs an active internet connection and an API ID + key, U2F will work with any FIDO U2F USB key out of the box, but can only be used when mailcow is accessed over HTTPS.
 - U2F and Yubi OTP support multiple keys per user.
 - As the third TFA method mailcow uses TOTP: time-based one-time passwords. Those psaswords can be generated with apps like "Google Authenticator" after initially scanning a QR code or entering the given secret manually.