Add version bytes section

Author: clarkmoody

bip-0049.mediawiki

@@ -66,6 +66,12 @@ To derive the P2SH address from the above calculated public key, we use the enca
     scriptPubKey: HASH160 <20-byte-script-hash> EQUAL
                   (0xA914{20-byte-script-hash}87)
 
+
+===Extended Key Version===
+
+When serializing extended keys, this scheme uses alternate version bytes. Extended public keys use <code>0x049d7cb2</code> to produce a "ypub" prefix, and private keys use <code>0x049d7878</code> to produce a "yprv" prefix. Testnet uses <code>0x044a5262</code> "upub" and <code>0x044a4e28</code> "uprv."
+
+
 ==Backwards Compatibility==
 
 This BIP is not backwards compatible by design as described under [#considerations]. An incompatible wallet will not discover accounts at all and the user will notice that something is wrong.