Update changelog

Author: athinab

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Add banner and an extra view for cookies options
 - Add corner ribbon that displays customisable text
+- Add this changelog file
 - Module discopower: Add style rules and logos for the IdPs:
   - eduTEAMS
   - EGI