update CHANGELOG.md

Author: Tomonobu Saito

CHANGELOG.md

@@ -14,6 +14,8 @@
       - CHANGED: allow routing past `barrier=arch` [#5352](https://github.com/Project-OSRM/osrm-backend/pull/5352)
       - CHANGED: default car weight was reduced to 2000 kg. [#5371](https://github.com/Project-OSRM/osrm-backend/pull/5371)
       - CHANGED: default car height was reduced to 2 meters. [#5389](https://github.com/Project-OSRM/osrm-backend/pull/5389)
+    - Misc:
+      - CHANGED: Reduce memory usage for raster source handling. [#5572](https://github.com/Project-OSRM/osrm-backend/pull/5572)
 
 # 5.21.0
   - Changes from 5.20.0