add derivation paths to example (#389)

.env.example

@@ -24,6 +24,9 @@ NOSTR_RELAYS=["wss://nostr-pub.wellorder.net"]
 # Wallet API port
 API_PORT=4448
 
+# Wallet default unit
+WALLET_UNIT="sat"
+
 # --------- MINT ---------
 
 # Network
@@ -38,8 +41,17 @@ MINT_INFO_CONTACT=[["email","[email protected]"], ["twitter","@me"], ["nostr",  "np
 MINT_INFO_MOTD="Message to users"
 
 MINT_PRIVATE_KEY=supersecretprivatekey
-# increment derivation path to rotate to a new keyset
-MINT_DERIVATION_PATH="0/0/0/0"
+
+# Increment derivation path to rotate to a new keyset
+# Example: m/0'/0'/0' -> m/0'/0'/1'
+MINT_DERIVATION_PATH="m/0'/0'/0'"
+
+# Multiple derivation paths and units. Unit is parsed from the derivation path.
+# m/0'/0'/0' is "sat" (default)
+# m/0'/1'/0' is "msat"
+# m/0'/2'/0' is "usd"
+# In this example, we have 2 keysets for sat, 1 for msat and 1 for usd
+# MINT_DERIVATION_PATH_LIST=["m/0'/0'/0'", "m/0'/0'/1'", "m/0'/1'/0'", "m/0'/2'/0'"]
 
 MINT_DATABASE=data/mint