walletinfo: add default wallet description

Author: ziggie1984

cmd/chantools/walletinfo.go

@@ -73,7 +73,10 @@ used and, if enabled with --withrootkey the BIP32 HD root key of the wallet. The
 latter can be useful to recover funds from a wallet if the wallet password is
 still known but the seed was lost. **The 24 word seed phrase itself cannot be
 extracted** because it is hashed into the extended HD root key before storing it
-in the wallet.db.`,
+in the wallet.db.
+In case lnd was started with "--noseedbackup=true" your wallet has the default
+password. To unlock the wallet set the environment variable WALLET_PASSWORD="-"
+or simply press <enter> without entering a password when being prompted.`,
 		Example: `chantools walletinfo --withrootkey \
 	--walletdb ~/.lnd/data/chain/bitcoin/mainnet/wallet.db`,
 		RunE: cc.Execute,