bip-322: clarify how the message is serialized

Author: kallewoof

bip-0322.mediawiki

@@ -61,7 +61,7 @@ The <code>to_spend</code> transaction is:
     vout[0].nValue = 0
     vout[0].scriptPubKey = message_challenge
 
-where <code>message_hash</code> is a BIP340-tagged hash of the message, i.e. sha256_tag(m), where tag = <code>BIP0322-signed-message</code>, and <code>message_challenge</code> is the to be proven (public) key script.
+where <code>message_hash</code> is a BIP340-tagged hash of the message, i.e. sha256_tag(m), where tag = <code>BIP0322-signed-message</code> and <code>m</code> is the message as is without length prefix or null terminator, and <code>message_challenge</code> is the to be proven (public) key script.
 
 The <code>to_sign</code> transaction is: