Update CHANGELOG.md (#1582)

Author: Baccata

CHANGELOG.md

@@ -7,6 +7,8 @@ Thank you!
 
 # 0.18.24
 
+* Adds missing nanoseconds in Document encoding of EPOCH_SECOND timestamps
+* Add support for `alloy#jsonUnknown`, allowing structures to capture unknown JSON fields in one of their members. 
 * Add `getMessage` implementation in `Smithy4sThrowable` which will be overridden in cases where the error structure contains a message field, but otherwise will be used to prevent a useless `null` result when `getMessage` is called.
 
 # 0.18.23