8.1.2 add comment clarifying Migrations

contracts/lifecycle/Migrations.sol

@@ -4,6 +4,7 @@ pragma solidity ^0.4.8;
 import '../ownership/Ownable.sol';
 
 
+// This is a truffle contract, needed for truffle integration, not meant for use by Zeppelin users. 
 contract Migrations is Ownable {
   uint public lastCompletedMigration;