1517: Updated CHANGELOG.md

Author: Vitaliy Boyko

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0).
 
 - java.lang.NoClassDefFoundError: org/codehaus/plexus/util/StringUtils [#1530](https://github.com/magento/magento2-phpstorm-plugin/pull/1530)
 - java.lang.Throwable: Must not start write action from within read action in the other thread - deadlock is coming [#1531](https://github.com/magento/magento2-phpstorm-plugin/pull/1531)
+- Custom theme detection [#1532](https://github.com/magento/magento2-phpstorm-plugin/pull/1532)
 
 ## 5.1.0