CHANGELOG entry for new Timestamp methods

Author: uint

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to
 - cosmwasm-std: Add `Timestamp::minus_seconds` and `::minus_nanos`.
 - cosmwasm-std: Add `Addr::as_bytes`
 - cosmwasm-std: Implement `std::ops::Sub` for `math::Decimal`
+- cosmwasm-std: Add `Timestamp::seconds` and `Timestamp::subsec_nanos`.
 
 ## [0.14.0] - 2021-05-03