backups: add samourai wallet

backups/samouraiwallet.md

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+## Samourai Wallet single seed multi-location backup scheme
+Documentation on Samourai Wallet recovery:  
+<https://support.samourai.io/article/18-restore-your-samourai-wallet-with-your-secret-words>  
+<https://support.samourai.io/article/8-restore-wallet-from-auto-backup-file>
+
+In case of restoring the wallet in different software (eg. Electrum) check  
+<https://walletsrecovery.org> for the derivation paths used.
+
+---
+### Components grouped together by the requirement for a full restore
+#### Full backup 1
+* Seed (12 words)
+* Passphrase (BIP39)
+#### Full backup 2 
+* Backup file (encrypted text)
+* Passphrase (BIP39)
+#### Full backup 3
+* Android device with the wallet loaded (locked with PIN codes)
+    * use a secondary, dedicated device for backup 
+    * have 2*8 digits PINs which are different from the primary device
+    * have a locked bootloader with the latest security patches
+* PIN codes to the Android Device AND Samourai Wallet
+    * test if the phone and the wallet can be unlocked with the PINs even after a restart
+
+---
+### Packages for a 2-of-3 setup
+#### Location 1
+- Seed (12 words)
+- Backup file (encrypted text)
+- PIN codes to the Android Device AND Samourai Wallet
+
+#### Location 2 
+- Passphrase (BIP39)
+- PIN codes to the Android Device AND Samourai Wallet 
+
+#### Location 3
+- Seed (12 words)
+- Android device with the wallet loaded (locked with PIN codes)