Update CHANGELOG.md with link to PR

Author: yaauie

CHANGELOG.md

@@ -1,5 +1,5 @@
 ## 3.3.2
-  - Added preview of ECS-v8 support with existing ECS-v1 implementation.
+  - Added preview of ECS-v8 support with existing ECS-v1 implementation [#76](https://github.com/logstash-plugins/logstash-filter-useragent/pull/76)
   - Internal: update to Gradle 7 [#75](https://github.com/logstash-plugins/logstash-filter-useragent/pull/75)
 
 ## 3.3.1