[DEWIF] add currency code

rfc/0013_Duniter_Encrypted_Wallet_Import_Format.md

@@ -36,8 +36,16 @@ This base64 string encodes a sequence of bytes whose structure is defined below.
 
 ## dewif bytes structure
 
-| version (4 bytes) | encrypted datas (any bytes) |
-|:-----------------:|:---------------------------:|
+| version (4 bytes) | currency code (4 bytes) | encrypted datas (any bytes) |
+|:-----------------:|:-----------------------:|:---------------------------:|
+
+## Currencies code
+
+| Currency | code       |
+|:---------|:-----------|
+| None     | 0x00000000 |
+| Ğ1       | 0x00000001 |
+| Ğ1-Test  | 0x01000001 |
 
 ## encrypted datas