Add changelog entry

Author: ukutaht

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 - Add tracker module to automatically track outbound links  plausible/analytics#389
 - Display weekday on the visitor graph plausible/analytics#175
 - Collect and display browser & OS versions plausible/analytics#397
+- Simple notifications around traffic spikes plausible/analytics#453
 
 ### Changed
 - Use alpine as base image to decrease Docker image size plausible/analytics#353