Update changelog

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased](https://github.com/usgs/waterdataui/compare/waterdataui-0.49.0...master)
+### Changed
+- The NWIS site service and sifta service now use aiohttp and are called concurrently in the monitoring_location view.
 
 ## [0.49.0](https://github.com/usgs/waterdataui/compare/waterdataui-0.48.0...waterdataui-0.49.0) - 2021-08-03
 ### Changed