add CHANGES.txt

Author: RamakrishnaChilaka

lucene/CHANGES.txt

@@ -280,6 +280,8 @@ Optimizations
 
 * GITHUB#15779: Improve BytesRefHash.add performance by optimize rehash operation (tyronecai)
 
+* GITHUB#15898: Optimize LongValueFacetCutter with leaf-local ordinal cache. (Ramakrishna Chilaka)
+
 Bug Fixes
 ---------------------
 * GITHUB#15754: Fix HTMLStripCharFilter to prevent tags from incorrectly consuming subsequent