Describe how to backup OTP codes

README.md

@@ -29,6 +29,7 @@ If you have a comment or suggestion, please open an [Issue](https://github.com/d
 - [Verify](#verify)
 - [Export](#export)
 - [Backup](#backup)
+  * [Backup OTP codes](#backup-otp-codes)
 - [Configure Smartcard](#configure-smartcard)
   * [Change PIN](#change-pin)
   * [Set information](#set-information)
@@ -1135,6 +1136,14 @@ $ doas mount /dev/sd2b /mnt/public
 $ gpg --armor --export $KEYID | doas tee /mnt/public/$KEYID.txt
 ```
 
+## Backup OTP codes
+
+There is a tricky way to have the same OTP codes on several YubiKeys with 
+[YubiKey Authenticator](https://www.yubico.com/products/services-software/download/yubico-authenticator/). For instance,
+if you've got YubiKey 5C and YubiKey 5 NFC then it's possible to install the authenticator to your PC and phone, insert
+YubiKeys to phone and PC and scan a 2FA QR code on both devices. In such situation, you will have the same OTP code on
+two YubiKeys what's good in case of a lost/stolen key.
+
 # Configure Smartcard
 
 **Windows** Use the [YubiKey Manager](https://developers.yubico.com/yubikey-manager) application (note, this not the similarly named older YubiKey NEO Manager) to enable CCID functionality.