Clarify the ERC20Snapshot contract comment (#1638)

contracts/drafts/ERC20Snapshot.sol

@@ -9,8 +9,8 @@ import "../token/ERC20/ERC20.sol";
  * @title ERC20 token with snapshots.
  * @dev Inspired by Jordi Baylina's MiniMeToken to record historical balances:
  * https://github.com/Giveth/minime/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol
- * Snapshots store a value at the time a snapshot is taken (and a new snapshot id created), and the corresponding
- * snapshot id. Each account has individual snapshots taken on demand, as does the token's total supply.
+ * When a snapshot is made, the balances and totalSupply at the time of the snapshot are recorded for later
+ * access.
  * @author Validity Labs AG <info@validitylabs.org>
  */
 contract ERC20Snapshot is ERC20 {