fix(docs): clarify direct minting format by adding zero padding detail

Author: fassko

docs/fassets/03-direct-minting.mdx

@@ -46,7 +46,8 @@ There are two supported formats:
 **32-byte memo** (recipient only):
 
 1. **8-byte prefix**: `0x4642505266410018` (`DIRECT_MINTING`)
-2. **20-byte recipient address**
+2. **4-byte zero padding**: `0x00000000`
+3. **20-byte recipient address**
 
 Anyone can execute, as no executor is specified.