bip-0300: Define endianness of upvote vector

Author: luke-jr

bip-0300.mediawiki

@@ -290,7 +290,7 @@ For example: if there are two sidechains, and we wish to upvote the 7th bundle o
 The version number allows us to shrink the upvote vector in many cases.
 Version 0x00 omits the upvote vector entirely (ie, 6 bytes for the whole M4) and sets this block's M4 equal to the previous block's M4.
 Version 0x01 uses one byte per sidechain, and can be used while all ACKed withdrawals have an index under 256 (ie, 99.99%+ of the time).
-Version 0x02 uses a full two bytes per sidechain, but it always works no matter how many withdrawl proposals exist.
+Version 0x02 uses a full two bytes per sidechain (each encoded in little endian), but it always works no matter how many withdrawl proposals exist.
 Version 0x03 omits the upvote vector, and instead upvotes only those withdrawals that are leading their rivals by at least 50 votes.
 
 If a sidechain has no pending bundles, then it is skipped over when M4 is created and parsed.