adding CHANGES.txt

Author: RamakrishnaChilaka

lucene/CHANGES.txt

@@ -150,6 +150,8 @@ Optimizations
 * GITHUB#15160: Increased the size used for blocks of postings from 128 to 256.
   This gives a noticeable speedup to many queries. (Adrien Grand)
 
+* GITHUB#15198: Optimized ForUtil.expand8 using the JDK Vector API. (Ramakrishna Chilaka)
+
 * GITHUB#14863: Perform scoring for 4, 7, 8 bit quantized vectors off-heap. (Kaival Parikh)
 
 Bug Fixes