Update HISTORY.md for thread-local stats

Summary: as titled

Test Plan: doitlive

Reviewers: sdong, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D63777

HISTORY.md

@@ -8,6 +8,7 @@
 
 ### New Features
 * Introduce NewClockCache, which is based on CLOCK algorithm with better concurrent performance in some cases. It can be used to replace the default LRU-based block cache and table cache. To use it, RocksDB need to be linked with TBB lib.
+* Change ticker/histogram statistics implementations to accumulate data in thread-local storage, which improves CPU performance by reducing cache coherency costs. Callers of CreateDBStatistics do not need to change anything to use this feature.
 
 ## 4.11.0 (8/1/2016)
 ### Public API Change