Explicitly refer to PATH_HASH_SIZE in docs

docs/payloads.md

@@ -273,7 +273,7 @@ Pull-based advert request. Sent to a specific node (via known path) to request i
 | Field         | Size (bytes)    | Description                                |
 |---------------|-----------------|--------------------------------------------|
 | sub_type      | 1               | 0xA0                                       |
-| target_prefix | 1               | first byte of target node's public key     |
+| target_prefix | 1               | PATH_HASH_SIZE of target node's public key     |
 | tag           | 4               | randomly generated by sender for matching  |
 
 ## ADVERT_RESPONSE (sub_type 0xB0)

docs/protocol_guide.md

@@ -383,7 +383,7 @@ Byte 0: 0x14
 **Command Format**:
 ```
 Byte 0: 0x39
-Bytes 1: Target Prefix
+Bytes 1: PATH_HASH_SIZE bytes (currently 1)
 Byte 2: Path Length
 Bytes 3+: Path (list of node hash bytes to reach target)
 ```