Add spec for binary token serialization

00.md

@@ -306,6 +306,18 @@ We serialize this JSON using CBOR which can be seen [here](https://cbor.nemo157.
 cashuBo2F0gqJhaUgA_9SLj17PgGFwgaNhYQFhc3hAYWNjMTI0MzVlN2I4NDg0YzNjZjE4NTAxNDkyMThhZjkwZjcxNmE1MmJmNGE1ZWQzNDdlNDhlY2MxM2Y3NzM4OGFjWCECRFODGd5IXVW-07KaZCvuWHk3WrnnpiDhHki6SCQh88-iYWlIAK0mjE0fWCZhcIKjYWECYXN4QDEzMjNkM2Q0NzA3YTU4YWQyZTIzYWRhNGU5ZjFmNDlmNWE1YjRhYzdiNzA4ZWIwZDYxZjczOGY0ODMwN2U4ZWVhY1ghAjRWqhENhLSsdHrr2Cw7AFrKUL9Ffr1XN6RBT6w659lNo2FhAWFzeEA1NmJjYmNiYjdjYzY0MDZiM2ZhNWQ1N2QyMTc0ZjRlZmY4YjQ0MDJiMTc2OTI2ZDNhNTdkM2MzZGNiYjU5ZDU3YWNYIQJzEpxXGeWZN5qXSmJjY8MzxWyvwObQGr5G1YCCgHicY2FtdWh0dHA6Ly9sb2NhbGhvc3Q6MzMzOGF1Y3NhdA
 ```
 
+#### Binary Token
+
+V3 and V4 Token can be transmitted in a binary format when applicable (for example when transmitting via NFC).
+For this the serialised token is prepended with a prefix and a version byte.
+
+```
+utf8("craw") utf8(<token_version>) <serialised_token>
+```
+
+- Token V3 Version: `utf8("craw") utf8("A") cbor(token_object)`
+- Token V4 Version: `utf8("craw") utf8("B") cbor(token_object)`
+
 [00]: 00.md
 [01]: 01.md
 [02]: 02.md