Update release notes

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

RELEASE_NOTES.md

@@ -10,7 +10,7 @@
 
 ## New Features
 
-<!-- Here goes the main new features and examples or instructions on how to use them -->
+- `LatestValueCache` now takes an optional `key` function, which returns the key for each incoming message, and the latest value for each key is cached and can be retrieved separately.  
 
 ## Bug Fixes